Drinking water is derived from two basic sources: surface waters, such as rivers and reservoirs, and groundwater. All water contains natural contaminants, particularly inorganic contaminants that arise from the geological strata through which the water flows and, to a varying extent, anthropogenic pollution by both microorganisms and chemicals. In general, groundwater is less vulnerable to pollution than surface waters. There are a number of possible sources of man-made contaminants, some of which are more important than others. These fall into the categories of point and diffuse sources. Discharges from industrial premises and sewage treatment works are point sources and as such are more readily identifiable and controlled; run off from agricultural land and from hard surfaces, such as roads, are not so obvious, or easily controlled. Such sources can give rise to a significant variation in the contaminant load over time. There is also the possibility of spills of chemicals from industry and agriculture and slurries from intensive farm units that can contain pathogens. In some countries, badly sited latrines and septic tanks are a significant source of contamination, especially of wells. Local industries can also give rise to contamination of water sources, particularly when chemicals are handled and disposed of without proper care. The run-off or leaching of nutrients into slow flowing or still surface waters can result in excessive growth of cyanobacteria or blue-green algae. Many species give rise to nuisance chemicals that can cause taste and odour and interfere with drinking water treatment. However, they frequently produce toxins, which are of concern for health, particularly if there is only limited treatment.

If treatment is not optimized, unwanted residues of chemicals used in water treatment can also cause contamination, and give rise to sediments in water pipes. Contamination during water distribution may arise from materials such as iron, which can corrode to release iron oxides, or from ingress of pollutants into the distribution system. Diffusion through plastic pipes can occur, for example when oil is spilt on the surrounding soil, giving rise to taste and odour problems. Contamination can also take place in consumers’ premises from materials used in plumbing, such as lead or copper, or from the back-flow of liquids into the distribution system as a consequence of improper connections. Such contaminants can be either chemical or microbiological.

A list of drinking water contaminants is provided below (Source:EPA);

Microorganisms

Contaminant Potential Health Effects from Long-Term Exposure Sources of Contaminant in Drinking Water
Cryptosporidium Gastrointestinal illness (such as diarrhea, vomiting, and cramps) Human and animal fecal waste
Giardia lamblia Gastrointestinal illness (such as diarrhea, vomiting, and cramps) Human and animal fecal waste
Heterotrophic plate count (HPC) HPC has no health effects; it is an analytic method used to measure the variety of bacteria that are common in water. The lower the concentration of bacteria in drinking water, the better maintained the water system is. HPC measures a range of bacteria that are naturally present in the environment
Legionella Legionnaire’s Disease, a type of pneumonia Found naturally in water; multiplies in heating systems
Total Coliforms (including fecal coliform and E. Coli) Not a health threat in itself; it is used to indicate whether other potentially harmful bacteria may be present5 Coliforms are naturally present in the environment; as well as feces; fecal coliforms andE. coli only come from human and animal fecal waste.
Turbidity Turbidity is a measure of the cloudiness of water. It is used to indicate water quality and filtration effectiveness (such as whether disease-causing organisms are present). Higher turbidity levels are often associated with higher levels of disease-causing microorganisms such as viruses, parasites and some bacteria. These organisms can cause symptoms such as nausea, cramps, diarrhea, and associated headaches. Soil runoff
Viruses (enteric) Gastrointestinal illness (such as diarrhea, vomiting, and cramps) Human and animal fecal waste

 

Disinfection By Products

Contaminant Potential Health Effects from Long-Term Exposure Sources of Contaminant in Drinking Water
Bromate Increased risk of cancer Byproduct of drinking water disinfection
Chlorite Anemia; infants and young children: nervous system effects Byproduct of drinking water disinfection
Haloacetic acids (HAA5) Increased risk of cancer Byproduct of drinking water disinfection
Total Trihalomethanes (TTHMs) Liver, kidney or central nervous system problems; increased risk of cancer Byproduct of drinking water disinfection

 

Disinfectants

Contaminant Potential Health Effects from Long-Term Exposure Sources of Contaminant in Drinking Water
Chloramines (asCl2) Eye/nose irritation; stomach discomfort, anemia Water additive used to control microbes
Chlorine (as Cl2) Eye/nose irritation; stomach discomfort Water additive used to control microbes
Chlorine dioxide (as ClO2) Anemia; infants and young children: nervous system effects Water additive used to control microbes

 

Inorganic Chemicals

Contaminant Potential Health Effects from Long-Term Exposure Sources of Contaminant in Drinking Water
Antimony Increase in blood cholesterol; decrease in blood sugar Discharge from petroleum refineries; fire retardants; ceramics; electronics; solder
Arsenic Skin damage or problems with circulatory systems, and may have increased risk of getting cancer Erosion of natural deposits; runoff from orchards, runoff from glass and electronicsproduction wastes
Asbestos (fiber > 10 micrometers) Increased risk of developing benign intestinal polyps Decay of asbestos cement in water mains; erosion of natural deposits
Barium Increase in blood pressure Discharge of drilling wastes; discharge from metal refineries; erosion of natural deposits
Beryllium Intestinal lesions Discharge from metal refineries and coal-burning factories; discharge from electrical, aerospace, and defense industries
Cadmium Kidney damage Corrosion of galvanized pipes; erosion of natural deposits; discharge from metal refineries; runoff from waste batteries and paints
Chromium (total) Allergic dermatitis Discharge from steel and pulp mills; erosion of natural deposits
Copper Short term exposure: Gastrointestinal distressLong term exposure: Liver or kidney damage

People with Wilson’s Disease should consult their personal doctor if the amount of copper in their water exceeds the action level

Corrosion of household plumbing systems; erosion of natural deposits
Cyanide (as free cyanide) Nerve damage or thyroid problems Discharge from steel/metal factories; discharge from plastic and fertilizer factories
Fluoride Bone disease (pain and tenderness of the bones); Children may get mottled teeth Water additive which promotes strong teeth; erosion of natural deposits; discharge from fertilizer and aluminum factories
Lead Infants and children: Delays in physical or mental development; children could show slight deficits in attention span and learning abilitiesAdults: Kidney problems; high blood pressure Corrosion of household plumbing systems; erosion of natural deposits
Mercury (inorganic) Kidney damage Erosion of natural deposits; discharge from refineries and factories; runoff from landfills and croplands
Nitrate (measured as Nitrogen) Infants below the age of six months who drink water containing nitrate in excess of the MCL could become seriously ill and, if untreated, may die. Symptoms include shortness of breath and blue-baby syndrome. Runoff from fertilizer use; leaking from septic tanks, sewage; erosion of natural deposits
Nitrite (measured as Nitrogen) Infants below the age of six months who drink water containing nitrite in excess of the MCL could become seriously ill and, if untreated, may die. Symptoms include shortness of breath and blue-baby syndrome. Runoff from fertilizer use; leaking from septic tanks, sewage; erosion of natural deposits
Selenium Hair or fingernail loss; numbness in fingers or toes; circulatory problems Discharge from petroleum refineries; erosion of natural deposits; discharge from mines
Thallium Hair loss; changes in blood; kidney, intestine, or liver problems Leaching from ore-processing sites; discharge from electronics, glass, and drug factories

 

Organic Chemicals

Contaminant Potential Health Effects from Long-Term Exposure Sources of Contaminant in Drinking Water
Acrylamide Nervous system or blood problems; increased risk of cancer Added to water during sewage/wastewater treatment
Alachlor Eye, liver, kidney or spleen problems; anemia; increased risk of cancer Runoff from herbicide used on row crops
Atrazine Cardiovascular system or reproductive problems Runoff from herbicide used on row crops
Benzene Anemia; decrease in blood platelets; increased risk of cancer Discharge from factories; leaching from gas storage tanks and landfills
Benzo(a)pyrene (PAHs) Reproductive difficulties; increased risk of cancer Leaching from linings of water storage tanks and distribution lines
Carbofuran Problems with blood, nervous system, or reproductive system Leaching of soil fumigant used on rice and alfalfa
Carbon tetrachloride Liver problems; increased risk of cancer Discharge from chemical plants and other industrial activities
Chlordane Liver or nervous system problems; increased risk of cancer Residue of banned termiticide
Chlorobenzene Liver or kidney problems Discharge from chemical and agricultural chemical factories
2,4-D Kidney, liver, or adrenal gland problems Runoff from herbicide used on row crops
Dalapon Minor kidney changes Runoff from herbicide used on rights of way
1,2-Dibromo-3-chloropropane (DBCP) Reproductive difficulties; increased risk of cancer Runoff/leaching from soil fumigant used on soybeans, cotton, pineapples, and orchards
o-Dichlorobenzene Liver, kidney, or circulatory system problems Discharge from industrial chemical factories
p-Dichlorobenzene Anemia; liver, kidney or spleen damage; changes in blood Discharge from industrial chemical factories
1,2-Dichloroethane Increased risk of cancer Discharge from industrial chemical factories
1,1-Dichloroethylene Liver problems Discharge from industrial chemical factories
cis-1,2-Dichloroethylene Liver problems Discharge from industrial chemical factories
trans-1,2-Dichloroethylene Liver problems Discharge from industrial chemical factories
Dichloromethane Liver problems; increased risk of cancer Discharge from drug and chemical factories
1,2-Dichloropropane Increased risk of cancer Discharge from industrial chemical factories
Di(2-ethylhexyl) adipate Weight loss, liver problems, or possible reproductive difficulties. Discharge from chemical factories
Di(2-ethylhexyl) phthalate Reproductive difficulties; liver problems; increased risk of cancer Discharge from rubber and chemical factories
Dinoseb Reproductive difficulties Runoff from herbicide used on soybeans and vegetables
Dioxin (2,3,7,8-TCDD) Reproductive difficulties; increased risk of cancer Emissions from waste incineration and other combustion; discharge from chemical factories
Diquat Cataracts Runoff from herbicide use
Endothall Stomach and intestinal problems Runoff from herbicide use
Endrin Liver problems Residue of banned insecticide
Epichlorohydrin Increased cancer risk, and over a long period of time, stomach problems Discharge from industrial chemical factories; an impurity of some water treatment chemicals
Ethylbenzene Liver or kidneys problems Discharge from petroleum refineries
Ethylene dibromide Problems with liver, stomach, reproductive system, or kidneys; increased risk of cancer Discharge from petroleum refineries
Glyphosate Kidney problems; reproductive difficulties Runoff from herbicide use
Heptachlor Liver damage; increased risk of cancer Residue of banned termiticide
Heptachlor epoxide Liver damage; increased risk of cancer Breakdown of heptachlor
Hexachlorobenzene Liver or kidney problems; reproductive difficulties; increased risk of cancer Discharge from metal refineries and agricultural chemical factories
Hexachlorocyclopentadiene Kidney or stomach problems Discharge from chemical factories
Lindane Liver or kidney problems Runoff/leaching from insecticide used on cattle, lumber, gardens
Methoxychlor Reproductive difficulties Runoff/leaching from insecticide used on fruits, vegetables, alfalfa, livestock
Oxamyl (Vydate) Slight nervous system effects Runoff/leaching from insecticide used on apples, potatoes, and tomatoes
Polychlorinated biphenyls (PCBs) Skin changes; thymus gland problems; immune deficiencies; reproductive or nervous system difficulties; increased risk of cancer Runoff from landfills; discharge of waste chemicals
Pentachlorophenol Liver or kidney problems; increased cancer risk Discharge from wood preserving factories
Picloram Liver problems Herbicide runoff
Simazine Problems with blood Herbicide runoff
Styrene Liver, kidney, or circulatory system problems Discharge from rubber and plastic factories; leaching from landfills
Tetrachloroethylene Liver problems; increased risk of cancer Discharge from factories and dry cleaners
Toluene Nervous system, kidney, or liver problems Discharge from petroleum factories
Toxaphene Kidney, liver, or thyroid problems; increased risk of cancer Runoff/leaching from insecticide used on cotton and cattle
2,4,5-TP (Silvex) Liver problems Residue of banned herbicide
1,2,4-Trichlorobenzene Changes in adrenal glands Discharge from textile finishing factories
1,1,1-Trichloroethane Liver, nervous system, or circulatory problems Discharge from metal degreasing sites and other factories
1,1,2-Trichloroethane Liver, kidney, or immune system problems Discharge from industrial chemical factories
Trichloroethylene Liver problems; increased risk of cancer Discharge from metal degreasing sites and other factories
Vinyl chloride Increased risk of cancer Leaching from PVC pipes; discharge from plastic factories
Xylenes (total) Nervous system damage Discharge from petroleum factories; discharge from chemical factories

 

Radionuclides

Contaminant Potential Health Effects from Long-Term Exposure Sources of Contaminant in Drinking Water
Alpha particles Increased risk of cancer Erosion of natural deposits of certain minerals that are radioactive and may emit a form of radiation known as alpha radiation
Beta particles and photon emitters
Increased risk of cancer Decay of natural and man-made deposits ofcertain minerals that are radioactive and may emit forms of radiation known as photons and beta radiation
Radium 226 and Radium 228 (combined) Increased risk of cancer Erosion of natural deposits
Uranium Increased risk of cancer, kidney toxicity Erosion of natural deposits