WITH INCREASING POLLUTION OF OUR WATER SOURCES, ATTENTION TO THE QUALITY OF DRINKING WATER BECOMES MORE IMPORTANT EVERY
DAY. WHETHER THE QUALITY OF DRINKING WATER IS ACCEPTABLE DEPENDS ON SEVERAL FACTORS ---HOW IT LOOKS, HOW IT TASTES, HOW IT SMELLS, AND HOW CLEAN AND SAFE IT IS.
CONTAMINANT LEVELS ESTABLISHED IN THE PENNSYLVANIA DEPARTMENT OF ENVIRONMENTAL PROTECTION REGULATIONS GOVERN
CONTAMINANTS THAT THREATEN PUBLIC HEALTH AS WELL AS THOSE AFFECTING THE WATER'S PALATABILITY, ITS AESTHETIC QUALITY, AND ITS POTENTIAL FOR CORROSION OR SCALING OF PIPES.
The physical characteristics of water include turbidity, color, taste and odor, temperature, and foamability (detergents).
The presence of suspended material such as finely divided organic material, clay, silt, and other inorganic material in water is known as turbidity. Turbidity is tested by measuring the amount of light scattered by particles in the water. As the number of particles increases, more light is scattered and a higher turbidity reading is obtained. The measuring instrument is called a nephelometer, and the readings are expressed as nephelometric turbidity units (NTU) or turbidity units. Turbidity in excess of 5 NTU is easily detected in a glass of water and is usually objectionable for aesthetic reasons.
Excessive turbidity is a problem for several reasons:
1. It protects microorganisms from chlorine and other disinfectants;
2. It acts as a food source for microorganisms, allowing them to survive and multiply;
3. It interferes with the maintenance of a chlorine residual;
4. It interferes with the test for coliform bacteria.
Clay or other inert suspended particles in drinking water drawn from groundwater sources may not adversely affect health, but water containing such
particles may require treatment to make it aesthetically suitable for its intended use. Following a rainfall, variations in groundwater turbidity may be considered an indication of surface or other introduced
pollution. Excessive turbidity must be removed by filtration.
Dissolved organic material from decaying vegetation and certain inorganic matter can cause color in water. Although color itself is not usually objectionable from a health standpoint, its presence is aesthetically objectionable and suggests that the water needs appropriate treatment.
Taste and Odor: Taste and odor in water can be caused by foreign matter such as organic compounds, inorganic salts, or dissolved gases. These
contaminants may come from domestic, agricultural, or natural sources. Water should be free from any objectionable taste or odor at the point of use.
Many natural and manmade substances will cause foam when water is agitated. The major cause of foaming is surfactants, which are synthetic organic chemicals used as the principal ingredient in modern detergents. Foaming is an undesirable property of drinking water because foaming agents may impart an unpleasant taste, cause frothing, and usually can be associated with contamination of groundwater.
Surfactants are the foaming agents which are measured to determine if drinking water has an acceptable foamability. The MCL* of 0.5 mg/l is based on
levels of foaming agents that would prevent the occurrence of visible foam.
Although foam itself is not generally hazardous, other possible hazardous materials may be present along with the foam. Water with high foamability
should be analyzed to determine what treatment may be required and to help determine the origin of contamination.
Foaming substances can be removed by conventional treatment consisting of coagulation/flocculation, sedimentation, and filtration, or by activated
COMMON CHEMICAL CHARACTERISTICS
The chemical characteristics of water include natural substances such as dissolved minerals and man made toxic metals and organic chemicals.
The alkalinity of water is a measure of its capacity to neutralize acids. Alkalinity is imparted to water by bicarbonate, carbonate and hydroxide components. Bicarbonates represent the major form of alkalinity, since they are formed in considerable amounts from the action of carbon dioxide upon minerals in the soil.
Although there is no MCL* for alkalinity, a range of 30 to 100 mg/l of Calcium Carbonate is desirable for finished drinking water
in order not to adversely affect taste and corrosivity. Alkalinity itself is not considered a health hazard.
Most waters contain some chloride. It can be caused by the leaching of marine sedimentary deposits and by pollution from sea water, brine or industrial and domestic wastes. Chloride concentrations in excess of about 250 mg/l usually produce a noticeable taste in drinking water. An increase in chloride content may indicate possible pollution from sewage sources, particularly if the normal chloride content is known to be low. Where only waters of very high natural chloride content are available, reverse osmosis or electrodialysis units may be used to produce potable water.
Copper is found in some natural waters, particularly in areas where copper has been mined. Excessive amounts of copper can occur in corrosive water that passes through unprotected copper pipes. Copper in small amounts is not considered detrimental to health, but will impart an undesirable taste to the drinking water. For this reason, the limit for copper is 1.0 mg/l.(1.3 mg/l by the copper/lead rule) Naturally occurring copper is rarely found in Pennsylvania at such high levels as to require treatment. Copper can be removed by conventional treatment consisting of coagulation/flocculation, sedimentation, and filtration, or by lime soda softening or reverse osmosis.
The tendency of a water to corrode pipes and fittings is health related as well as being of economic importance, since the materials released into water by corrosion may include lead, cadmium, and other toxic metals. The corrosivity of water is not easily measured. However, equations have been developed that reasonably predict the tendency of water to corrode on the basis of temperature, total dissolved solids, calcium content, hardness, pH, and alkalinity. These equations indicate the calcium carbonate stability of water the tendency to either deposit or dissolve calcium carbonate (CaCO3), the most common scale forming compound. In most cases, a water that is neutral or slightly scale forming is preferred.
Water that is excessively corrosive can be stabilized made noncorrosive by the addition of lime and soda ash to increase the pH and alkalinity,
or by the addition of polyphosphates or silicates to form protective coatings on the pipe walls. These treatment processes are relatively complex, requiring trailed operators and regular monitoring.
In some areas of the country, water sources contain natural fluorides. Where the concentrations fall within a certain range, the incidence of dental caries has been found to be below the rate in areas without natural fluorides. It has been established that the presence of about 1 mg/l of fluoride in a water supply will help to prevent tooth decay in children. The effect is the same whether the fluoride occurs naturally or is added to the water during treatment. The optimal fluoride level for a given area depends on air temperature, since that is what primarily influences the amount of water people drink. Optimal concentrations from 0.7-1.2 mg/l are recommended. Excessive fluorides in drinking water supplies may produce fluorosis (mottling) of teeth, which increases as the optimum fluoride level is exceeded. Higher levels adversely affect bone structure.
Excess fluoride can be removed by ion exchange using bone char or activated alumina, a relatively complex process requiring trained operators. Reverse
osmosis is a simpler alternative that may be appropriate for smaller systems having access to waters of high fluoride content.
Hard water retards the cleaning action of soaps and detergents, causing an expense in the form of extra work and cleaning agents. Furthermore, when hard water is heated it deposits a hard scale on heating coils, cooking utensils, and other equipment with a consequent waste of fuel. The scale formed by hard water coats the inside of distribution system piping, which can eventually cause significant reductions in its water carrying capacity. Soft water, on the other hand, tends to be more corrosive.
A hardness of 75 to 100 mg/l as CaCO3 is usually considered optimal for domestic water. Water harder than 300 mg/l as CaCO3 is generally unacceptable.
Lime soda ash or ion exchange softening processes can be used to produce acceptably soft water.
Calcium and magnesium salts, the most common cause of hardness in water supplies, are divided into two general classifications: carbonate, or
temporary, hardness and noncarbonate, or permanent, hardness. Carbonate hardness is called temporary hardness because heating the water will usually remove it. When the water is heated, bicarbonates break down
into insoluble carbonates that precipitate as solid particles which adhere to a heated surface and the inside of pipes. Noncarbonate hardness is called permanent hardness because it is not removed when water is
heated. Noncarbonate hardness is due largely to the presence of the sulfates and chlorides of calcium and magnesium in the water.
Small amounts of iron are frequently present in water because iron in present in the soil and because corrosive water will pick up iron from unprotected pipes. The presence of iron in water is considered objectionable because it imparts a brownish color to laundered goods and affects the taste of beverages such as tea and coffee. The Pa. DEP MCL for iron is 0.30 mg/l. A variety of methods are available for iron removal. Conventional treatment consisting of coagulation/flocculation, sedimentation, and filtration are generally effective. Chemical oxidation or aeration followed by filtration may also be required, and certain softening processes can be used.
There are two reasons for limiting the concentration of manganese in drinking water: 1) to prevent aesthetic and economic damage to property and 2) to avoid any possible physiological effects from excessive intake. The domestic water user finds that manganese produces a blackish color in laundered goods and affects the taste of beverages, including coffee and tea. The Pa. DEP limit for manganese is 0.05 mg/l. Essentially the same treatment processes used to remove iron are used to reduce manganese levels. However, manganese is harder to remove than iron, because its precipitation is more pH dependent.
Nitrate (NO3) can cause methemoglobinemia (infant cyanosis, or "blue baby disease") in infants who have been given water or fed formulas prepared with water having a high nitrate concentration. A domestic water supply should not contain nitrate concentrations in excess of 10 mg/l (expressed as nitrogen). High levels found in shallow wells may be an indication of seepage from septic systems or livestock manure deposits. In some polluted wells, nitrite (NO2) will also be present in concentrations greater the 1 mg/l and is even more hazardous to infants. When the presence of high nitrite concentration is suspected, the water should not be used for infant feeding. Ion exchange and reverse osmosis can be used to remove excess nitrate and nitrite.
Organic Chemicals: Organic chemicals include pesticides, herbicides, trihalomethanes, and volatile synthetic organics. Careless use of
pesticides and herbicides can contaminate water sources and make the water unsuitable for drinking. The use of these chemicals near wells is not recommended. Maximum contaminant levels for several common
pesticides and herbicides have been established.
are a group of organic compounds that form when chlorine reacts with humic and fulvic acids (natural organic compounds that occur in decaying vegetation). Trihalomethanes, potential carcinogens (cancercausing agents), should not exceed 0.10 mg/l in drinking water.
Volatile Synthetic Organics:
occur in the waste products of various industrial processes and are commonly found in ground waters near heavily industrialized areas. At high levels these chemicals have accuse toxic effects, and at trace levels some are suspected of being carcinogenic. Limits for several of the volatile organics are currently included by the EPA as regulated contaminants.
Organics can generally be removed by adsorption with activated carbon. Trihalomethanes can often be avoided by altering the chlorination process. Most
volatile organics can be eliminated with aeration. The effectiveness of reverse osmosis units on organics has not been fully investigated. For all organics, protection of the water source is an important
pH is a measure of the hydrogen ion concentration in water. It is also an indication of acid or alkaline content. The pH scale ranges from 0 to 14, with 7 indicating neutral water. Values less than 7 indicate sharply increasing acidity, and values greater than 7 indicate sharply increasing alkalinity. The pH of water in its natural state varies from 5.5 to 9.0. Determination of the pH value assists in the control of corrosion, the determination of proper chemical dosages, and adequate control of disinfection. The treatment processes used to control corrosivity and scaling involve pH adjustment.
The sodium content of drinking water is generally of little concern to consumers except those on sodium restricted diets. The amount of sodium in drinking water is insignificant compared to the sodium normally consumed in the average diet. When it is necessary to know the precise amount of sodium present in a water supply due to dietary constraints, a laboratory analysis should be made. The usual low sodium diets allow for 20 mg/l sodium in the drinking water. When this limit is exceeded, persons on low sodium diets should seek a physician's advice on diet and sodium intake.
When water is softened by the ion exchange method, the amount of sodium is increased when sodium chloride is the regenerant. For this reason, water that has
been softened should be analyzed for sodium if a precise record of an individual's sodium intake is recommended. High sodium levels can be reduced with reverse
osmosis or electrodialysis units.
Waters containing high concentrations of sulfate caused by the leaching of natural deposits of magnesium sulfate (Epsom salts) or sodium sulfate (Glauber's salt) may be undesirable because of their laxative effects. Sulfate content should not exceed 250 mg/l. Reverse osmosis, ion exchange, or electrodialysis can be used to reduce sulfate concentrations.
Total Dissolved Solids:
Total dissolved solids (TDS, also called total filterable residue or total dissolved residue) is a measure of the water's content of various dissolved materials. Water with no dissolved solids usually has a flat taste, whereas water with more than 500 mg/l TDS usually has a disagreeably strong taste. Depending on the chemical nature of the dissolved solids, reverse osmosis, or lime soda softening may be used to reduce TDS content.
Arsenic, barium, cadmium, chromium, lead, mercury, selenium, and silver can all cause serious health problems. Lime soda softening and reverse osmosis can both be used to reduce the concentrations of toxic metals. Precipitation with alum is also effective for certain metals. Lead can be a serious problem even if not found in raw water. Corrosive waters may leach lead from pipes and fixtures, often exceeding the 0.015 mg/l maximum safe limit.
Zinc is found in some natural waters, particularly in areas where zinc has been mined. Zinc is not considered detrimental to health at or near 5 mg/l but it will impart an undesirable taste to drinking water. For this reason, the MCL for zinc is 5 mg/l Softening, reverse osmosis, ion exchange, or electrodialysis will reduce zinc concentrations.
Water for drinking and cooking purposes must be free from disease causing organisms. These organisms include bacteria, protozoa, viruses, and worms.
The specific disease causing organisms present in water are not easily identified, and the techniques for comprehensive bacteriological examination are complex and time consuming. It has been necessary, therefore, to develop tests that indicate the relative degree of contamination in terms of a single, easily performed test.
Because many of the microorganisms that cause disease in man are transmitted through the fecal wastes of infected individuals, the most widely used method
of testing the bacteriological quality of water involves testing for a single group of bacteria that are always present when fecal contamination is present. This group of bacteria, the coliform group, inhabits
the intestinal tract of man, but is also found in most domestic animals, birds, and certain wild species. The methods used to test specifically for coliform are the membrane filter test
and the multiple tube fermentation test. A third test, the heterotrophic (standard) plate count, determines the total number of
bacteria in a sample that will grow under certain conditions.
Some groundwater sources, if properly protected and developed, can meet bacteriological drinking water standards without treatment. However, disinfection is
a recommended safeguard for noncommunity systems and required treatment for community systems. Chlorination of ground water also introduces a disinfectant residual that helps maintain bacteriological quality of
the water in the distribution system.
Water from surface sources should always be disinfected, usually by chlorination, before it is supplied to the public. For both ground and surface
water, protection of the source from contamination should be an ongoing priority. In ground water sources, iron bacteria can cause problems with staining and tastes and odors. Proper well drilling
procedures will prevent the entrance of iron bacteria into a new well, and iron bacteria in an existing well can usually be eliminated by temporarily introducing a high chlorine concentration.
A well serving more than 25 people or having at least 15 connections is considered a public water supply and must comply with Pennsylvania Safe
Drinking Water Regulations.
*Maximum Contaminant Level
This information has been obtained from the Pennsylvania D.E.P. Public Water Supply Manual, Part I