1. When is water hard, what problems does this cause and how can they be solved?

Water hardness is due to calcium and magnesium salts in water in abnormally high concentrations.

The problems of hard water are seen in the home when cooking some foods (e.g. vegetables). These can turn hard and bitter. Hard water also stains bathroom fittings (toilets and bathtubs) and kitchen fittings as well. Likewise, hard water reduces the formation of lather when we bath or wash clothes.

From the point of view of health, drinking hard water does not cause any problems.

Hard water can be treated by "softening it" by chemical processes, which can be carried out in a treatment system in the home. Small systems exist containing some special resins that retain the salts causing the hardness when water is passed through them.

Consumption of contaminated water can be a source of serious illnesses. The chlorine is a barrier against that risk, because chlorine is one of the better disinfectants that can be employed in the production of drinking water.

If drinking water comes to our table with chlorine, then we can be certain that our water is free of harmful germs.

The chlorine concentration in water varies with the diverse treatments and with the location of houses to the water distribution networks. However, those concentrations must be between 0.5 and 5 mg of chlorine/liter of water.

In populations that have drunk water contaminated with arsenic there is evidence of health effects. The illnesses caused by arsenic are: palm-plantar hyperkeratosis, whose symptoms are skin pigmentation and callousness on the palms of the hands and the feet, hyper- and hypopigmentation of the face, neck and chest, and cancer of the skin, lungs, liver, kidney and bladder.

The symptoms of severe intoxication by arsenic are: abdominal pain, vomiting, diarrhea, muscular pain and weakness with skin redness. These symptoms are often followed by numbness and itching of the extremities, muscular deadness and the appearance of skin eruptions, white stripes in the nails called Mees'lines, and progressive deterioration in sensory and motor responses and irritation of the breathing organs.

The countries that have water with high concentrations of arsenic are Bangladesh, Chile, Mexico, Argentina, Mongolia, Thailand and the United States. Worldwide there are more than 30 million persons that consume water with a content of arsenic that is higher than the recommended level (10 µg As/L) of the World Health Organization (WHO).

4. Why is fluorine in drinking water beneficial?

Fluorine in water prevents tooth decay. Although decay can be diminished using toothpaste with fluorine, rinsing or dietary fluorine supplements, the best way is by fluoridation of water supplies since this does not require the conscious intervention of the individual.

Water fluoridation programs in centralized systems (treatment plants) reaching a concentration of 1 ppm (1 mg/L) are considered to be of important benefit for public health.

Yes, fluorine is a chemical element that is utilized to elaborate raticides. The chemical compounds for raticides are sodium fluoroacetate (C₂H₂FNaO₂) and 2- fluoroacetamide (C₂H₄FNO).

The raticides are sold in powder form and are used by mixing with some rat food to cause their death.

However, the fluorine compounds used in raticides are not the same that are employed in water fluoridation. Although the most important thing is the concentration of fluorine in water. The concentrations of fluorine in drinking water are not a risk, but they are beneficial for health.

It is an illness known as methemoglobinemia, due to the presence of methemoglobin in the blood that is caused by the presence of nitrates.

This illness occurs when nitrates are converted to nitrites by the bacteria in the digestive system of the children. The nitrites react with the hemoglobin to form methemoglobin. The hemoglobin is a chemical substance that carries oxygen from lungs to different parts of the body, while the methemoglobin does not carry out this function.

When the oxygen level decreases in a child’s body, he literally suffocates, showing a blue color in his skin mainly around mouth and eyes.

This illness affects children under 6 months by the following reasons: 1. Infants have a lower stomach acidity which allows growth of bacteria capable of converting nitrates to nitrites. 2. Infants still have considerable amounts of fetal hemoglobin which is more easily converted to methemoglobin that the adult hemoglobin. 3. Infants are deficient in certain enzymes that are able to convert methemoglobin back to normal hemoglobin. 4. Children's body weights are about 80 % water, while the adult of 65%. This means children consume much more water than adults and if water contains nitrates the children will consume more quantity of these than adults.

Because natural water is out of people’s reach and to deliver it to houses requires a series of installations and costly equipment. Likewise it requires to be treated to assure that its quality is suitable for human consumption. These treatments generate costs that should be covered by the user.

Furthermore in paying for water consumption, this also includes the cost of treating the wastewater generated by the consumption water.

There are 3 kinds: (1). Water generated by use in domestic and commercial activities is about 8% of total water consumption in the world (2). Water generated by industrial activities represents around 23%, and (3). Water generated by agricultural activities constitutes approximately 69%.

Water is contaminated by the introduction of potentially pathogenic organisms or toxic substances that vary from different uses. Water sources are contaminated by discharge of untreated wastewater from domestic, commercial, industrial or agricultural activities. The latter can cause aquatic extinction and proliferation of bad smells in the environment. For these reasons, fresh water loses its quality.

Industry contaminates with heavy metals toxic for humans such as arsenic, lead, cadmium, mercury, and chromium. Industry also uses ionic compounds such as cyanides and nitrates that can be discharged in the wastewater. Water use as a coolant raises temperatures higher than normal for water courses into which they are discharged.

Agricultural activities employ fertilizers for plants and pesticides for protection against pests, and irrigation water collects the wastes of these chemical compounds.

A sanitary engineer is the professional that acts in the field of the environmental engineering. His activities are oriented to management in the areas of environmental sanitation, water treatment for human consumption and networks of sewerage, wastewater treatment and final wastewater destinations, solid waste management, sanitary installations of interiors, and food hygiene.

Other activities of the sanitary engineer are studies of environmental impact of the development projects that are carried out. The purpose is that of conserving and to protect the environment to achieve a better life quality.

A sanitary engineer also works in the basic sanitation area, to supports actions that increase the cover and improve the quality of the services of potable water and sewerage, and waste management.

Sand filter is based on the use of sand as a filtering material. The filter works with sand grains of selected diameter graded from 0.15 to 0.45 mm. Filters remove particles bigger and smaller than this range. Bigger particles are held by the sifting physical effect and smaller ones by the adhesion effect to the surface of the superficial layers of the filtering element.

The objective of filtering by sand filter is the separation of particles in suspension and the harmful microorganisms present in the water otherwise destined for the human consumption.

Water turbidity is produced by very light and small particles when they "coagulate".

To coagulate is to form bigger particles, which can then be eliminated by sedimentation. This is done by finely divided material or colloidal particles present in it.

The coagulation process is carried out by the addition to water of substances with positive charges to neutralize the negative charge of colloids. The rest of the turbidity formed by bigger particles is added to the jellied mass of the formed coagulum.

The resulting coagulum has a bigger density than the colloidal particles, which results in easy elimination by sedimentation.

The most commonly used coagulants are aluminum or iron salts: ferric sulfate (Fe₂(SO₄)₃) and ferric chloride (FeCl₃), aluminum sulfate (Al₂(SO₄)₃), and aluminum chloride (AlCl₃).

Because seawater is salty due to the presence of dissolved salts in large quantities in the form of magnesium, calcium, sodium, potassium, chloride, bromide, fluoride, and sulfate ions. The amount of total dissolved solids in seawater is around 35,000 mg/liter, and water for human consumption must have a maximum of 1,000 mg/liter according to the WHO.

Furthermore, seawater is not only unpleasant for the palate but some of the dissolved substances, such as magnesium sulfate are highly purgative and can cause vomiting and convulsions. Seawater has different properties than freshwater.

No, it is not difficult. In fact there are many methods for the desalination of seawater. The most common are: reverse osmosis, distillation, multiple effect distillation, multiple stage flash distillation, and freezing. The problem is that all they are expensive and they require high consumption of energy.

Safe water for human consumption can be found in any house tap that is provided from a public network water supply or bottled mineral water that they are sold in the grocery stores. In the absence of these two sources, water can be taken from springs, rivers or lakes, but before drinking it must be disinfected.

In general, no. Most surface water (rivers and lakes) is slightly turbid. The turbidity can originate from different kinds of matter in suspension, such as: fine sand, clay, slime or microorganisms, and colloidal particles that are particles of organic matter from leaf decay, cortexes and other vegetable substances in decomposition.

Spring water, at its source, is considered pure, because it comes directly from the subsoil and is free of contamination by human beings. During its flow it is exposed to contamination caused by the animal waste, wild birds and by the human activity.

River and lake waters are used for transportation by fishermen and tourists who can contaminate the water with pathogenic organisms that can cause illness to people.

Normally, no. Tap water has already been treated and is suitable for human consumption. However, if it is heard that the public network of water supply is contaminated with pathogenic germs then it is recommended to boil it before drinking.

In small communities or individual systems where the water supply system is not taken care of or where the water provided has not received some treatment, it should be considered to boil the water before drinking it.

THM is the abbreviation of trihalomethane. These are compounds that are formed when adding chlorine to water to disinfect it and they react with some organic substances present in water. An example of THM is chloroform (CHCl₃).

In prolonged consumption of water with high trihalomethanes content, humans can acquire cancer. Therefore the water quality regulations for human consumption have established a maximum allowable limit allowing of this substance.

Some of the disinfectant pills used in water disinfection are: "My Health", "Aquatabs", "Halozone", "Potable Agua or Globaline", "Chlor-floc", and "Pill with silver ions", etc.

Most of the disinfectant pills contain chlorine compounds, except the pills with silver ions. The pills ‘’My Health’’ contain dichlorineisoanuric acid or sodic troclosen and ‘’Aquatabs’’ pills are composed of an inert base, effervescing, excipients of pharmaceutical compounds and food, and of a dichlorineisocianurate ingredient.

Rainwater is pure only in rural areas, where there aren’t industries. The gases emitted by the industries go up in the atmosphere and react with the rainwater being formed; the so- called acid rain. This acid rain damages plantations and is not suitable for drinking. In very densely populated zones rainwater is exposed to contamination by solid material in the atmosphere which contains contaminants such as heavy metals: mercury, zinc, lead, arsenic and pathogenic microorganisms.

However, in areas away from this contamination source rainwater can be used for human consumption. In fact, in many regions of the world it is done so. In any case, it is always advisable to disinfect water before drinking.

Water provides an important component in the fulfillment of metabolic functions of the living organisms. The daily intake of water should be 3% of the body weight. That is to say, a person weighing 80 kg requires 2.4 liters water per day.

The human body loses water daily in urine, breathing, transpiration, and in defecation. A person of 80 kg will lose 1.2 liters (50%) in urine, 0.4 liters (17%) in breathing, 0.6 liters (25%) in transpiration and 0.2 liters (8%) in defecation.

Yes. However, it is always good to be certain that the water comes from a safe source, such as a water treatment plant, that has been well operated and controlled.

In some small towns treatment plants consist of a simple sediment tank and no disinfection is done before water is distributed through the pipe line to the users. In this case it is good to boil before drinking and disinfecting with disinfectants substances.

Boron is used in many human activities, the most intensive are: detergent manufacturing, wood treatment for its preservation, glass and porcelain manufacturing, soldering, silvering and many metallurgic processes. That is to say, boron is an element in common use in industry and that as such generates considerable water body pollution. The solutions for cadmium, silvering, copper, lead, nickel, and zinc that use BF₄ have an equivalent in boron concentration
between 16,000 and 33,000 mg/L. Even in drainage water measured levels are up to 6 mg/L.

However despite this relatively high frequency in the occurrence of boron in water, and given the high concentrations of boron which are cycled in water courses, the world literature does not present many treatment technologies for boron.

There is a distillation and steam condensation method and then passage of the condensate through ceramic-filled columns. Water containing 20,000 mg/L of boron is reduced to less than 3 mg/L. However this method is not practical to for drinking water treatment plants.

Neither the biological nor traditional coagulation and flocculation treatments that are carried out in treatment plants can remove boron from water.

Of relative efficiency can be mentioned, the ionic interchange with specific resins (Amberlite IRA-943 – Rohm and Haas) and the use of reverse osmosis (RO).

The (RO) method is popular in industrialized countries, and permits removal of about 60% of the boron from water. However, all the limitations, special requirements, and direct and associated costs that are involved in the use of this technology should be kept in mind if it is desired to utilize RO to reduce high boron levels.

To sum up, there is neither an economical nor an efficient method for removal of boron in drinking water treatment plants.

The WHO states in its Guidelines for Drinking Water Quality: "drinking water treatments do not adequately eliminate this element".

Answer to first question is YES.

In fact, if corpses are buried close to the coast, it is possible that many elements that come from decomposition as bacteria, organic matter, nitrogen, and phosphorus go to the seawater. However this will depend on two things. Firstly, the kind of soil. If the soil is of the sandy kind, which has a high freatic nappe, then it is much more permeable to the contamination than if the ground is hard and compact. Secondly, the distance of the land from where the corpse is buried to the coast. In "normal" soils, contamination will not move more than a few hundred meters.

Thus, it is difficult to determine the contamination of an area, although analyzing the specific place, the distance from water, and the kind of soil we can get to a more precise idea.

The question that derives from the one above and which is much more important is:

Is it important that eventual contamination?

Answer is NO.

If you bury the 12,000 pets in the same area close to the sea coast and therefore concentrate the great mass of corpses, then certainly that is going to create a focus of high contamination. But if the burials are done in the gardens of the houses, then certainly there will not be.

For more than a thousand million years our planet has developed and utilized with great efficiency an ecological mechanism to deal with so many corpses. You worry about the dogs and cats but think that there are trillions and trillions more bacterias than dogs. Since humans evolved, possibly some 100,000,000,000 men and women have died, and more rabbits, rats, fowls, deers, insects, arthropods, etc., etc.

If you worry about corpses buried near the lake or sea, you know that many more beings die in the sea than on land? and what happens with all this dead mass of things?

It is that marvellous ecological mechanism of the Earth that you know, and which is very simple: living tissue made of carbon, nitrogen and phosphorus are oxidized into carbonic anhydride, nitrates and phosphates. These last three substances are utilized by sea and land plants to growth and feed. Plants are eaten by herbivorous animals and these last by carnivorous ones. So much some as other already have closed the circle and they have prepared the living tissue from the basic components.

Here your question becomes interesting. Since those animal masses (human included) and plants (that having a common origin with living beings, have compositions very similar) were not buried then all the planet would die!

Therefore, the best advice is, when your animal pet dies, it is better to bury it in the house yard rather than throwing it away at the municipal rubbish or burning it.

This is the best thing that can be done for the planet in memory of your dog or cat.

Silica (SiO₂) is silicon dioxide and it is the principal component of a common kind of sand and fine rock sand. The natural concentration in raw water is in the range of 1 to 30 mg/L, even though high concentrations can be found up to 100 mg/L. Very salty water (influenced by seawater) can have values over 1,000 mg/L.

Silica is inconvenient in water, because it forms deposits inside equipment, pipe lines, etc. and also because it is difficult to treat.

The treatment method is by using resins (basic hard anionics) for ionic interchange or reverse osmosis.

From the health point of view, silica in water is not bad. For that reason the WHO does not consider it neither include it in its guidelines for drinking water quality. It is a parameter that is not incorporated in the water quality norms of countries.

The problem (and enough serious) of the silica is that when inhaling it, it causes lung illnesses including cancer of lung.

The NIOSH (National Institute for Occupational Safety and Health of USA) analyzes the potential and real damages to health for distinct substances, and about silica it says:

"Silica when it is taken in any of its several forms, such as crystalline quartz, amorphous silica soil (diatomaceous earth, diatomites) or colloidal silica jelly is chemically and biologically inert".

For those waters that have an excessive concentration of fluorides ("fluoride" and not "fluorine", because that is the form in which the element fluorine is present in the water), there are several ways of reducing it to the recommendable levels for a good dental health of the population.

However, it should be clear that if the population is too big, the tendency is to try to find another source of supply, since normally surface water does not have high fluoride concentrations and to avoid treatment of large amounts of water.

It is a material of interchange and functions like a common and simple interchanger.

In the United States of America this material is widely used, and is used in the majority of the world where there are problems with fluorides.

It is also an ionic interchange technique. The difference is that the interchangeable material is ground and ungreased bone.

This technique was perfected in Argentina. The SNAP (National Service of Potable Water) in the 70’s installed many water treatment plants in the provinces of La Pampa, Buenos Aires, and Cordoba.

There is very good information about all this in the COFAPYS of Argentina.

The bonechar is bone coal. This technique is similar to the one mentioned above, and the base material is prepared bone as well. The difference is that the material has undergone an additional treatment: it has been carbonized. With this it earns in taste, and the water does not have the possibility of adding taste to broth, which sometimes occurs when using ground bone.

There is no experience in Argentina. Bone coal was used in the United States of America but as a second choice instead of activated alumina.

It is used at present. This technique removes all the fluoride (as of the majority of the other present ions). For that reason part of the water is treated like this and then raw water is mixed.

This option is the most recommendable but unfortunately it is an expensive process that requires much energy and qualified personal.

The presence of chlorine is important in water to assure the good disinfection and as residual to prevent contamination in the distribution network. Therefore, there should always be a certain quantity of chlorine in distributing water, in water that arrives at the houses, and water that the users drink.

The minimum residual level must be 0.5 mg/L of chlorine per liter of water, even though, there are other related demands that must accompany that concentration, such as the minimum contacting time, turbidity, and the pH of water.

At the maximum level it is estimated that the threshold is 5 mg/L. This has sanitary reasons, but also because users detect lower levels by taste and smell. Generally, when the value of 5 mg/L is reached there have already been complaints and refusal to drink the disinfected water.

This question lacks a true meaning if some other considerations or other specifications are not added.

As stated in the text that accompanies the question, Sudan has a low consumption rate per capita and that the criterion of to whom does the question apply will be a factor of efficiency.

In reality it is not it.

That the "provision" (liters/inhabitant x day) is low, can mean that the people have awareness of the water value, and preserve, take care and do not squander it; however this could suggest that water supply is not enough; or that treatment plants do not provide the necessary quantity to cover all inhabitants needs, and for that reason the water use is low. This demonstrates that the indicator of "low consumption", by itself, is not enough and therefore can signify diametrically opposite things.

To consider a country a good potable water manager, it is necessary to consider the integrated cycle of water use. That is to say, how the country manages the hydrographic basins, water treatment, what percentage of coverage for the population, how are the water supplied and the quality of water supply.

So that a water supply be considered of good standard, we should consider the "five Cs" (in Spanish): quantity (how much water does the population have available globally and per capita), continuity (the water net has to have 24 hours of the day constant pressure. Sometimes it is not true in the rural areas of many developing countries and this is a cause of contamination), quality (the obvious quality of water, specially in the microbiological parameters), closeness (it is not the same to have water inside the house or 100 meters away in a public source) and confidence (the positive perception of the water user that the water supply system is dependable, and other water sources should not be preferred by the users, perhaps because they are less reliable than the one already used for the system).

Without impairment of all it said, and in answering the question about "which country better manages its potable water" it can be said that by regulations and norms of quality, the importance of water treatments systems, by the quality of the water delivered, by the controls that are done upon the water, the First World Countries have clear advantage upon the remainder in this area.

The question of high concentrations of algae in water has no easy answer. The specific situation in each case must be known, such as water quality and the contaminating concentrations. An adequate answer requires a careful study.

In spite of that, general ideas can be given.

First, Cyanophyte algae are also known as Mixophytes, Schyzophytes, or Cyanobacteria, better known as "blue algae". Some of those names mentioned above refer to the affinity between algae and bacteria in their prokaryotic organization, their size being the main difference. Algae create the plankton and even though not as small as bacteria, it is undoubtedly very small. Then we have a species whose volume is large and whose individuals are small. Any way (if it be taken as "many" or as "few") it will cause problems in the areas where it develops, and in the drinking water treatment plants that utilize water with algae.

Problems arise from the already detected smell and taste, blocking of filters (mainly slow filters), and the toxin production that can be a risk to human health. These toxins (called "cyanotoxins") are the products of some of the cyanobacteria.

Although there is no doubt about the relation between cyanotoxins and human health, there is little information about human illness in relation with them and it is unknown if deaths are due to them. Any way, water consumption with high concentrations of these species, and with eventual lethal effects, certainly would be rejected by users before drinking, due to the simple organoleptic problems (appearance, smell and taste).

With no detriment to it, algae present a problem that is not always simple to solve, because the best way of attacking the problem is by evaluation and management of water sources. The excessive growth of algae is due to the presence of high concentrations of nutrients, mainly phosphorous, in lakes and dams. Therefore, what needs to be done is to ascertain which are the practices of the river or basin users that contribute so much nutrients and to work for their reduction (it should be done by educating, legislation, or police action that can take a long time).

When the problem arrives at the water treatment plants, there are a series of possible treatments, from the use of microgratings and sieves at the entrance, prechlorination, rough prefiltering or grave, airing, flotation by air pressure, and a very careful coagulation and flocculation. Those methods are possible. Although none is easy those who are faced with algae prefer always to fight the water problem outside treatment plants before it arrives inside.

The ideal thing is that algae do not arrive at the plant.

29. In my country there has been a proposition to modify the national legislation for drinking water quality and in one specific parameter they have gotten aside from the values given in "WHO guidelines for drinking water quality". In this case it has been proposed to give a maximum value of chloroform concentration of 30 microgram per liter instead of the indicated value of 200 microgram per liter in WHO guidelines. How can this be?

It is important to mention that such "Guidelines" are not an official legal document, it is only a reference document.

Given that appreciation, the WHO proposes in the mentioned document the figure for the "Guideline- Value".

The "Guideline- Value" is a value that represents the concentration of a constituent that does not pose in any significant risk to the health of the consumer over a lifetime of consumption.

However the same document, in its second edition of 1995 warns:

"The water quality defined by the Guidelines is such that it is suitable for human consumption and for all domestic purposes, including personal hygiene. However, water of a higher quality may be required for some special purposes".

However, it is important to understand the principle that governs these Guideline values which are the basis of understanding problems that can arise from the preparation of national norms with distinct values that are offered in the WHO document.

This principle is that those guidelines values are exactly what the name indicates: "guides", "hints", "suggestions".

Under no circumstances are the guides impositions or strict limits and insurmountable.

Above all, the countries through their specialized agencies (normally Health Ministries) are the ones that have the ability and legal and moral power of making norms in accordance with the best understanding of their professional, technical and governmental officers.

And that should be sought to know and to understand the reasons by a health institution themselves aside from the values suggested by the WHO.

Other more exigent values than the ones proposed by the WHO do not necessarily improve the water quality for human consumption and very possibly they incur higher costs in the treatment and operation of the plants.

But the analysis should go beyond any particular case to seek the relations with other components in raw water, in problems of disaffection by-products, in the health situation of the inhabitants, regional epidemiology, etc.

This analysis is the one that can give reasons for a narrow limit.

In those cases it is recommended that a developed process of scientific evaluation gives a better relationship between the standard agencies and potable water supplier, to arrive at values that safeguard the population’s health, and taking into consideration the technical situation, economics, and resources in general of the providers.

30. I have a conductivity meter that only expresses results in siemens units or microsiemens and I want to know the conversion factor to take it into ohm or mho units.

Conductivity is expressed in 1/ohm x cm

The inverse of the ohm (resistance unit) is mho. Therefore:

1/ohm = 1 mho

Since potable water or fresh water has low values, conductivity is normally expressed in micro mhos/cm (m mho/cm).

In the international system of units (IS) Siemens (S) is defined as mho. Therefore:

1 m mho/cm = 1 m S/cm

Some equipment measures conductivity in millisiemens/meter (mS/m).

In that case the conversion is:

1 mS/m = 10 (m S/cm

"Coagulation" is an important water treatment process for its human consumption, because there is no another way of eliminating the turbidity of raw water. This technology requires the addition of substances that through a physico-chemical mechanism permits the gathering of small and light particles. The added particles produce bigger ones (called "floccules") that are easily eliminated by decantation. There are several substances for coagulating and they received the generic name of "coagulants".

A coagulant works by a hydrolization mechanism and creation of physico-chemical structures, where the developing compounds by the process itself are covered by electrical loads that attract the loads of other smaller particles creating together bigger ones.

This mechanism is not particularly for one substance. It can be applied to many substances that work with the mechanism and that are used with this.

Aluminum sulfate (also called "alumina"), ferric chloride, and a series of natural polyelectrolites (derived from amylum, cellulose, and alginates) and synthetic polyelectrolites consist of simple monomers that polymerize in high molecular weight substances and that are classified as anionic, cationic and non ionic being denominated coagulants. Aluminum Polychloride (PACl), referred in the question above is a recently used coagulant.

The PACl is a liquid product. Its name "polychloride" refers to its real chemical composition. This is not a definite composed formula but a mixture of polymers or aggregates of hydroxide polymers of aluminum chloride with the formula Al_n(OH)_mCl_(3n-m) with 0<m<3n.

The PACl contains variable concentrations of aluminum chloride, and this concentration is conventionally expressed as "percentage weight of Al". The rank goes from 2.5% to 13%. The PACl can be made of several substances with aluminum content including metallic aluminum, trihydrated aluminum, aluminum chloride, aluminum sulfate and their respective combinations. Depending of the manufacturing processes, the final product can contain sodium, calcium and magnesium salts, as chlorides and sulfates.

Commercially the PACl is presented as a clear liquid, acid and highly corrosive for most exposed metals. For the PACL delivery and storage special containers should be prepared covered with synthetic rubber, anticorrosive plastic reinforced with glass fiber (FRP), ceramic, PTFE PDVF, polyethylene, polypropylene and PVC. Steel, aluminum, nickel, copper, and bronze are not recommended, because they are attacked by the material.

PACl is highly caustic it can cause burns as well as skin and eye irritation. When it being handled, protective clothes such as gloves, boots, and trousers made of rubber must be worn. In addition, protecting glasses and facial masks must also be worn. (AWWA-Standard for liquid polyaluminium chloride- 1997).

From the point of view of its utilization as a coagulant, it has good characteristics because it has a high electric charge before mixing with the water for treating (this last is typical of aluminum sulfate). Moreover, it has a moderate molecular mass, which is a desirable property.

As is known the two parameters that influence the coagulation process are pH and temperature.

In comparison with aluminum sulfate, which is an excellent coagulant and the one for which we have most information, there exist the following differences:

Comparatives studies about the removal of organic material between the PACl and alumina show that PACl is more effective in a greater of pH and temperature range.

In relation to this last parameter, Exall et al (in their article: Using coagulants to remove organic matter – Journal AWWA Nov 2000) show that temperature variation affects alumina more than PACL, verified in the necessary concentrations to carry out an equal coagulating with the two compounds.

In the table you can see that there is not great difference if we talk about moderate or warm environmental temperatures, but when treating cool water it is necessary to utilize double doses of alumina rather than PACI and also it is necessary to add to this the costs of correction of pH.

A search of providers has been done in a typical Latin American city, and it was found that there are local distributors for the two components. The costs are as follows (In $US per ton):

Alumina: $350                 PACl: $850

A simple analysis shows that it is much more economical to work with aluminum sulfate if water is warm or hot. In areas where temperature is cold, costs are more or less comparable.

Without impairment of this cost analysis (that in most cases has a strong impact in the decision of purchasing), it is also important to have in consideration the operation parameters.

With this point of view, it is advisable to utilize aluminum sulfate, because its management is known, there is much experience as well as a bibliography related to its form of use.

Its management is less dangerous and it does not require sophisticated dosification equipment or personnel protection. All those characteristics are taken in consideration specially if systems do not belong to big cities or consolidated companies and well mounted. It is possible also, that the provision of alumina is easier to find, because it is a more popular product than the PACl.

For all the good properties of PACl it should not be underestimated and it should be recommended to look for aluminum sulfate as the first option.

Products used during the potabilization processes may react on water itself or on the health of people using that drinking water. All of this requires four types of evaluations.

At first, there is a physical-chemical evaluation in which the product is tested for physical and chemical specifications that the manufacturer claims to be true. For example, if such solution with such concentration can lower the turbidity in such units, or that a compound alkalinizes adequately water of low pH, or reducing the concentration of a specific metal to a determined level. Among these evaluations are some about quality products, others that show certified concentrations shown on their labels, or that the products do not contain trace elements considered dangerous to health (for example, lead or mercury free).

A second kind of evaluation is about its behavior as an agent in biological (or microbiological) contaminations. This means, for example, verifying the bactericide power of the product that the manufacturer claims their products have, such as bacteria like E. Coli; Total Coliform; aeruginose pseudomone, criptosporidium, etc.

A third type of evaluations are social or communitarian. This means evaluation of the behavior of the community or part of it or facing the use of the product. For example, the response of a small community from a social point of view (acceptance, use, rejection, easiness in its use, perception of its qualities and cost, etc.) facing implementation of a disinfection program by hypochlorite distributed by driblets.

Finally, evaluations necessary for water treatment are clinical and epidemiological researches that tell people if drinking water with a specific concentration of the product during a certain period of time does not affect the health of the community. These are also called toxicological risk assessments. It is important to enlighten up that these assessments are sometimes, long-terms, difficult to undergo and many times very expensive.

CEPIS, as a center for sanitary engineering and environmental sciences has a certified laboratory and trained personnel that can undergo the requirements of any of the three big groups of evaluation mentioned here. And it routinely undergoes these evaluations.

However, in relation to the evaluations that have to do with health, it is important to say that it is neither CEPIS’ competence, nor the Center has the capacity to undergo the clinical evaluations described in the last point. But, above all, neither Ministry of Health nor OPS representatives nor a regional center are the organizations that must carry out these studies or prepare the assessments over the hazards of a determined compound.

In the countries, the ones giving certificates (authorization for the use of a product) should be the Government through specific Institutions (most of the times, the Health Ministry). This Ministry is neither responsible for the search for evidence of harmlessness or for undergoing the assessments. On the contrary, it must be the manufacturer or the product distributor who has the obligation to do the research and to hand in a file containing all the information related to the toxicology of the product.

Frequently, researches are of acute, sub acute and chronic toxicity and these must be done under strict regulations and by skilled personnel and certified institutions.

The Ministry should have assessment mechanisms of such files and act accordingly.

Sodium dichloroisocyanurate (NaDCC) is, chemically speaking, sodium salt of 1,3,5 Triazine – 2,4,6 (1H,3H,5H) Trione. When this compound is dissolved in water it generates hypochlorose acid and sodium cianurate.

Owing to its physical characteristics of great stability, easiness in manipulating, simpleness in its dosage, and good percentage of disinfectant per product weight, NaDCC is used in swimming pool disinfections and in water refrigerating systems for the avoidance of algae proliferation.

At times, it has been used as disinfectant for human consuming water, because hypochlorose acid is a well-studied compound, considering it not only one of the most important and well-known disinfectants at present, but also this acid is not dangerous to health al levels normally used for water disinfection.

An interesting research presented in the AIDIS Congress in 1998 (Lima) by Jose Antonio de Angelis et al ("Disinfections of water with substances based on NaDCC "), shows that waters disinfected with that compound had a better acceptance by the community that underwent the research which compared disinfections of NaDCC vs. hypochlorite. The research shows that 70% of the community preferred the use of pills with NaDCC against the droplets because it is easier to handle, there is greater security in its use and storage, generates fewer odors and practically has no flavor.

All of this seems to suggest that the product above is ideal for water treatment for human consumption. However this is not true. Strictly speaking, even though we know about hypochlorose acid, but there is not much security about the use of sodium cianurate and the danger it can cause to human health. Even though the scientific evidence does not condemn the use of the product for specific health problems, neither enough evidence exists to assure the absolute innocuity and safety in its use.

That means, in spite of its notorious advantages, there isn’t enough qualitative and quantitative information to assure conclusively that the compound is free of risks to the users health.

With regard to isocianurate, the final position of the WHO is not to guarantee the use of this compound in water disinfections. (At least for now and until more evidence proves its complete innocuity).

Besides the WHO’s position; sometimes, in many countries where there is the need for water disinfection in case of emergencies, the use of NaDCC is allowed. In those cases it is understood that the use of the compound is only temporarily.

This would take us to a situation, which could be defined as:

"Emergency Disinfections, yes. Systematic Disinfections, no".