Drinking-Water Quality - What To Look Out For

Updated: Nov 27, 2020

Water is an essential requirement for life. The average adult needs around 3 litres of water every day. However, not all water is safe for drinking.

Diseases that are acquired through the intake of unsafe drinking water has made a major impact on public health. Fortunately, nowadays interventions are in place to assure access to safe drinking water. The subsequent improvements in drinking water quality afforded a lot of positive effects on the health of the general population.

Water is about the safest thing you could put inside your body, so long as it adheres to rigorous quality control measures. There is no associated significant health risk to the consumption of water. Furthermore, safe drinking water can be used for a variety of purposes including personal hygiene.

The greatest threat to water quality is microbial contamination. However, chemical contamination of drinking water has also led to several serious health concerns.

Quality of drinking water

The common folk would assess the quality of water based on their senses. If the water would appear aesthetically unappealing to the consumer then they might avoid consumption. There may even be instances wherein the consumer might opt to drink water from unsafe sources because these sources were better aesthetically.

Aside from the looks, the water needs to taste and smell good as well. Chlorinated water may sometimes smell like chlorine and would have a slight taste of it. Unchlorinated water, on the other hand, is absent of this undesirable smell and taste. In this case, the consumer may opt to drink unchlorinated water which would place them at risk of acquiring water-borne diseases.

What are the qualities of good drinking water?

  • Water should not taste and smell odd. This is the first thing that people would notice so extra effort should be made to ensure that drinking water tastes the way it is supposed to. It is the responsibility of the water supplier to make sure that their water tastes and smells good because their customers can only assess the water through their senses. In general, the customers don’t own or know how to assess water quality scientifically.

  • Water should not be too turbid or coloured. Even if the cause of the turbidity and colour is not hazardous, consumers would think that it is.

Why is it not good to drink tap water?

In most developed countries, tap water is as safe as bottled water. For example, the United States has the Food and Drug Administration to oversee bottled water and the Environmental Protection Agency to assess tap water. However, both organizations use safety standards that are almost identical.

In other countries, this might be different. Tap water is still unsafe for drinking in most 3rd world countries. Bottled water, which underwent better treatment and purification processes, is safer than tap water in developing countries.

Even though tap water is safe in 1st-world countries, there are people who are vulnerable to water contaminants at a level that is tolerable to most. Individuals who are taking immunosuppressant drugs, those who have HIV or AIDS, and those who are undergoing chemotherapy are all vulnerable. Pregnant women, children, and older adults are all vulnerable to contaminants as well.

Guidelines for drinking water quality

To ensure that our drinking water adheres to a certain standard, guidelines are in place for suppliers to follow.

WHO guidelines for drinking water quality

To ensure safe drinking water, the World Health Organization, suggests three components in implementing a preventive approach to maintaining water quality.

The first component is the ‘health-based targets based on an evaluation of health risks’. These are goals and objectives relating to maintaining water quality. They are established based on risk assessments of waterborne pathogens and other waterborne hazards.

The second component is the Water Safety Plans. The focus of this component is on assessing a suppliers’ capability to deliver their goods, in this case, water, to the consumer while maintaining quality and meeting the goals and objectives set in the first component. Another important aspect of the Water Safety Plans is the operational monitoring of the measures intended for maintaining drinking-water safety. Water Safety Plans include the management and documentation of all operational actions undertaken in ensuring the safety of a suppliers’ drinking-water. The final aspect of the Water Safety Plans is the risk assessment and risk management steps used to evaluate and assess all of the actions taken to ensure the safety of drinking water from the supplier’s catchment to the consumer’s receiving end.

The third component is surveillance. Both the authorities and the suppliers themselves are responsible for constantly monitoring the safety and quality of the drinking water that the suppliers would provide. This is important because the early detection of any harmful contamination means early intervention and better risk mitigation.

Drinking water standards

The Environmental Protection Agency or EPA has a long list of water contaminants that will negatively affect the quality of drinking water. For a drinking-water to meet the EPA’s standards, then they must not contain contaminants or possess acceptable amounts.

EPA Drinking water standards

These are the items present in EPA’s National Primary Drinking Water Regulations that are worth mentioning:


We’re going to be using some terminologies that WHO came up with.

  • Maximum Contaminant Level Goal (MCLG) - The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety and are non-enforceable public health goals.

  • Maximum Contaminant Level (MCL) - The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to MCLGs as feasible using the best available treatment technology and taking cost into consideration. MCLs are enforceable standards.

  • Maximum Residual Disinfectant Level Goal (MRDLG) - The level of a drinking water disinfectant below which there is no known or expected risk to health. MRDLGs do not reflect the benefits of the use of disinfectants to control microbial contaminants.

  • Treatment Technique (TT) - A required process intended to reduce the level of a contaminant in drinking water.

  • Maximum Residual Disinfectant Level (MRDL) - The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants.


  • Total coliforms (including faecal coliform and E. coli).

  • The MCLG for Total coliforms including faecal coliform and E. coli is zero. Meaning that some health risks would be observed if there are coliforms, faecal coliforms, or E. coli present in the drinking-water even if they are present in small amounts. In other words, there shouldn’t be any coliform, faecal coliform, or E. coli present in drinking water.

  • Except for some serotypes of E. coli., coliform, faecal coliform, and E. coli are not pathogenic in general. However, their presence in drinking water signifies faecal contamination. Water contaminated with faecal material is highly likely to contain pathogens that are spread through the feco-oral route.

  • Coliforms are naturally present in the environment while faecal coliforms and E. coli could only come from the faecal matter of both humans and animals.

  • Cryptosporidium

  • All microorganisms that could contaminate and make drinking-water unsuitable for drinking has an MCLG of zero. Even if they are present in minute amounts in drinking water, there is still a possibility that a person who drinks that water would acquire an infection due to that microorganism.

  • This microorganism can cause gastrointestinal illnesses such as cramps, vomiting, and diarrhoea.

  • When cryptosporidium-containing faecal matter mixes with drinking water; then the drinking water may carry the pathogen as well.

  • Giardia lambia

  • Like all of the microorganisms in EPA’s National Primary Drinking Water Regulations, the MCLG of Giardia lambia is zero as well.

  • This pathogen may cause symptoms similar to that of cryptosporidium.

  • Giardia lambia ends up in drinking-water when the water gets contaminated with faecal matter from an infected human or animal.

  • Legionella

  • MCLG of Legionella is zero

  • They are naturally present in water but are spread through airborne water droplets. Cooling towers, a piece of equipment used as air-conditioning units for large buildings, that are contaminated with the legionella bacteria may generate mist or vapour containing the bacteria and infect those who inhale it.

  • When your respiratory tract gets infected with Legionella you may develop Legionnaires’ disease.

  • Viruses (enteric)

  • the MCLG of enteric viruses is also zero

  • Detecting enteric viruses in water is rarely done. When drinking water is contaminated with faecal matter, it is assumed to contain enteric viruses.

  • Enteric viruses are capable of causing several gastrointestinal illnesses.


  • Chlorine dioxide (ClO2)

  • Chlorination is the process of adding chlorine to drinking water to control the number of microbes present in it to make it safer for drinking. However, this process may introduce chlorine dioxide to the drinking-water.

  • It has an MRDL and MRDLG of 0.8 which is quite low. This means that drinking-water is only safe for consumption if the amount of chlorine dioxide present in it does not exceed 0.8 mg/L.

Disinfection byproducts

  • Bromate

  • Some water suppliers would use ozone to disinfect their water. Naturally occurring bromine present in water gets oxidized by the ozone into bromate.

  • This disinfection byproduct has an MCLG of zero. This means that if bromate is present in drinking water in small amounts it would cause health issues to the consumers. Furthermore, this also means that there shouldn’t be any bromate present in drinking-water.

  • Long term exposure to minute amounts of bromate can increase your risk of acquiring cancer.

  • Chlorite

  • The usage of chlorine dioxide in the treatment of drink-water can result in the production of chlorite. This reaction is favoured under alkaline conditions.

  • The MCL for Chlorite is 1.0 mg/L, safe drinking-water shouldn’t possess chlorite that exceeds that concentration.

  • The MCLG for chlorite is 0.8 mg/L, this means that if drinking-water were to reach this chlorite concentration, or exceeds it, consumption of this drinking-water would affect the health of the consumer negatively.

Inorganic chemicals

  • Arsenic

  • Ideally, water should not have any arsenic present in it (MCLG - 0 mg/L). However, if the complete elimination of arsenic is not possible a concentration of 0.010 mg/L is acceptable (MCL - 0.010 mg/L).

  • Soil contains arsenic naturally in amounts that are usually harmless. However, there are also natural deposits of arsenic which may contain harmful levels of the chemical. Aside from natural deposits, glass and electronics production may increase arsenic concentrations in soil. Damage to pipelines and run-off that ends up in the water reservoir is the most common reasons as to why drinking water gets contaminated with arsenic.

  • Long-term exposure to arsenic will result in skin and circulatory problems, and increased risk for cancer.

  • Antimony

  • According to the Environmental Protection Agency or EPA, Antimony has an MCLG and MCL of 0.006 mg/L. In other words, the concentration of antimony in drinking water should not exceed 0.006 mg/L for it may affect a person’s health negatively.

  • Petroleum refineries, smelting facilities, and porcelain production facilities may release antimony in high amounts as a byproduct of their activities.

  • Long-term exposure to antimony may lead to unhealthy blood cholesterol levels which increase a person’s risk for developing cardiovascular diseases.

  • Beryllium

  • Beryllium is a rare element that hardly exists in its pure form. The Environmental Protection Agency has found some evidence that Beryllium may pose a cancer risk to humans when ingested. Due to this, the EPA decided that Beryllium should have an MCLG and MCL of 0.004 mg/L.

  • Water reservoirs or broken pipelines may become contaminated from the beryllium discharge produced by metal refineries and coal-burning factories.

  • Long-term exposure to beryllium may increase your risk of developing cancer and may also cause intestinal lesions.

  • Cadmium

  • Facilities that deal with zinc, lead, and copper extraction would release cadmium as a byproduct of their activities. Cadmium is also present in significant amounts in pesticides and manures. Run-off from farms and the aforementioned facilities may introduce cadmium to water reservoirs which would ultimately end up in our drinking water. Broken pipelines that run beneath soils that are highly contaminated with cadmium would also introduce cadmium to our drinking water.

  • EPA has set cadmium’s MCLG and MCL to 0.005 mg/L

  • Long-term exposure to cadmium would result in Kidney damage.

  • Cyanide

  • Is a deadly chemical that may come in various forms; it can be crystalline such as sodium cyanide (NaCN) or potassium cyanide (KCN) or gas such as hydrogen cyanide (HCN) or cyanogen chloride (CNCl). They are naturally present in the soil. However, the activity of certain industries like paper, textiles, plastics, and metallurgy may increase the amount of Cyanide in the soil. They may contaminate drinking-water reservoirs through the action of run-off. Broken pipelines may also lead to cyanide contamination of drinking water.

  • MCLG and MCL = 0.2 mg/L

  • Long-term exposure to cyanide may result in nerve damage and or thyroid problems.

  • Lead

  • Lead may contaminate drinking water when the household plumbing gets corroded. Run-off from areas containing high concentrations of lead may reach drinking-water reservoirs.

  • Lead exposure is harmful to infants and children for it can slow down their mental development. For adults, long-term exposure to lead may damage the Kidney and may lead to the development of high blood pressure.

  • Ideally, Lead should be completely absent from drinking-water (MCLG = 0 mg/L). Once it reaches a concentration of 0.015 mg/L treatment techniques to remove lead from the drinking-water should be applied immediately (MCL = 0.015 mg/L).

  • Mercury

  • Mercury is naturally present in the soil. They may be present in high amounts within natural deposits. Aside from this, mercury may be present in high amounts around landfills that get dumped with mercury-containing materials such as batteries, around mining sites, and around fossil fuel combustion sites. Rain may erode the water in these mercury-rich areas and may end up in water reservoirs or seep through the ground and enter broken pipelines.

  • MCLG = 0.002 mg/L and MCL = 0.002 mg/L

  • Long-term exposure to mercury may cause kidney damage.

  • Selenium

  • Selenium is actually a micronutrient. The recommended amount that you should consume in a day is 55 micrograms. You may go beyond 55 but you must not exceed 400 micrograms. Selenium toxicity is rare but you should be wary with brazil nuts. Each nut contains 68 to 91 micrograms of Selenium. If you eat around 7 nuts or more, you may experience Selenium toxicity.

  • Selenium toxicity may occur if it is present in drinking-water at very high amounts. Drinking-water may possess very high amounts of Selenium when it is contaminated with run-off from petroleum refineries, natural deposits, and mining discharges.

  • MCLG = 0.05 mg/L and MCL = 0.05 mg/L

  • Long-term exposure may lead to circulatory problems, numbness in fingers and toes, loss of fingernails and hair.

  • Thallium

  • Thallium may be present in high amounts around ore-processing sites, electronic factories, glass-making factories, and pharmaceutical factories. Rain may dissolve the thallium and carry it downwards through the soil, a process known as leaching. Once this chemical leaches through the soil, it may end up in well water, water reservoirs, or enter the opening of damaged pipelines.

  • MCLG = 0.0005 mg/L and MCL = 0.002 mg/L

  • Long-term exposure may lead to kidney, intestine, or liver problems, hair loss, and negative changes in the blood.

Organic chemicals

Generally, all organic chemicals present in EPA’s National Primary Drinking Water Regulations have a Maximum Contaminant Level Goal or MCLG of zero. This means that these organic chemicals may pose a public health risk even if it is present in minute amounts. Below is a complete list of all known organic chemicals that may contaminate drinking-water:





Benzo(a)pyrene (PAHs)


Carbon tetrachloride





1,2-Dibromo-3-chloropropane (DBCP)









Di(2-ethylhexyl) adipate

Di(2-ethylhexyl) phthalate


Dioxin (2,3,7,8-TCDD)






Ethylene dibromide



Heptachlor epoxide





Oxamyl (Vydate)

Polychlorinated biphenyls (PCBs)







2,4,5-TP (Silvex)





Vinyl chloride


These are the radionuclides present in water:

  • Alpha particles

  • Beta particles and photon emitters

  • Radium 226 and Radium 228 (combined)

  • Uranium

As a general rule of thumb, there shouldn’t be any radionuclides in drinking water, so their MCLG is 0 mg/L.

In rare cases where radionuclides do contaminate the drinking water, the source is almost always from natural deposits. However, beta particles and photon emitters may come from man-made sources.

Long term exposure to these radionuclides would make you more susceptible to cancer.


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