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Posted on 31 August 2017 by Editorial team
Posted in FluksAqua Community, FluksAqua insights, Innovation, Utility management, Wastewater Management, Water and wastewater community, Tagged chemical contaminants, drinking water quality,


The World Health Organization (WHO) issued an addendum to its fourth edition of the 2011 Drinking-water Quality (GDWQ) in February 2017. GDWQ, which includes guideline levels for chemical contaminants in drinking water, is meant to serve as a health based framework for the water quality standards around the world and is recognized as the United Nations’ official position on drinking water quality.


While Canada and the U.S. are major participants in the WHO process, both countries are completely independent when it comes to setting their water quality standards and guidelines. Health Canada (guidelines) and the U.S. Environmental Protection Agency (enforceable standards) determine the water quality specifications in their respective countries. The WHO guidelines are adopted as standards in most nations but there can be differences.

Joseph Cotruvo is a long-time member of the WHO GDWQ committee and was involved in the recent revisions. Before establishing his own water consultancy, he spent 24 years at the USEPA as the director of its Drinking Water Standards Division and as a director of USEPA’s Risk Assessment Division. He describes the changes as minor adjustments but they do have influence around the world.

The addendum includes new guidelines for perchlorate and barium and removes the 4-chloro-2-methyphenoxyacetic acid (MCPA) guideline for lack of significant risk from drinking water. Chlorate and chlorite guidelines were reevaluated and reaffirmed. Guidelines for bentazone, chlorine dioxide, dichlorvos, diquat and dicofo were not added, although health-based values for several pesticides were added. The 2017 addendum also provides substantial information on turbidity, water safety plans, drinking water microbiology, quantitative microbial risk assessment and radionuclides.

According to Cotruvo, the most interesting change is in the perchlorate guideline since the U.S. is trying to produce its own perchlorate standard while under court order to do so. The WHO guidelines are well above the current EPA perchlorate advisory numbers in the U.S. as well as some state determined values.

“Perchlorate risks are tied to iodine deficiency, and the primary concerns are pregnant women and infants with insufficient iodine intake,” he explains. “Perchlorates compete with iodine which supports thyroid function. Iodized salt was introduced in the US almost 100 years ago to reduce the risk of goiter caused by iodine deficiency. So if there is sufficient dietary iodine, perchlorate in drinking water is not much of a problem. Pregnant women are usually given supplements as a precaution.”

Cotruvo points to the perchlorate dilemma in the U.S. as a good example of when judgment needs to be part of the process. The guidelines are scientifically based but he encourages water decision makers to use professional judgment within their national construct when it comes to determining their water treatment quality goals.

“There are no drastic changes in the first addendum but the entire document is full of tremendously valuable information and I would encourage water operators and utilities to read and use it as a resource,” says Cotruvo.  

It is available for free download from the WHO website.

Cotruvo points to incidents where the guidelines have been mistakenly used to issue boil water and other notices when it was probably not necessary. For example, 400,000 residents of Toledo, Ohio were told not to drink or contact the water because of an algae bloom on Lake Erie in 2014. The water utility was advised by the State to make the call when the microcystin number briefly went above the WHO guidelines. However, the WHO guideline was for lifetime exposure – not one day.


“Except for microbial contaminants, a measurement above the guideline does not automatically mean the water is not safe – there is a substantial margin of safety  built into all of the WHO guidelines,” says Cotruvo.

“The numbers are not meant to be black and white so water operators and regulators should understand the guidelines and then determine how they should proceed using good judgment and the circumstances. In my experience, many water engineers feel that they are not in a position to make independent health risk judgments, so they will make their decisions based upon published values and regulatory directives, and if standards are being exceeded, it is their responsibility to meet the legal limit. Slightly elevated levels of standard or guideline does not automatically mean a crisis.”

Even when standards are developed, there are sometimes different interpretations and values. The USEPA often uses different assumptions than the WHO when it comes to calculating drinking water values. Cotruvo says it reflects different procedures and assumptions so judgment and scientific consensus is an important part of the process. Both results are considered “safe”.

The WHO addendum reflects a move to a new approach for pesticides. Rather than including a long list of pesticides guidelines, WHO will often produce “benchmark values” rather than formal guidelines. The WHO was concerned that some countries could misinterpret guidelines and cause unnecessary monitoring and other costs. Cotruvo says that makes it easier for national regulators and water providers to focus on local pesticides rather than a long list of items that are not relevant to their area of country.

Cotruvo expects additional updates when the WHO issued their second addendum in 2018-19 and fifth edition in 2020-21.

“There are not a lot of major changes because there is a considerable amount of history and experience with the content of the GDWQ,” he explains.

“I would expect Chrome VI and algal toxins to be major components in the next revision.”



Barium: a chemical element and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element, but as salts like barium chloride or barium sulfate.

Bentazone: a herbicide categorized under the thiadiazine group of chemicals and appears slightly brown in colour.

Chlorine dioxide: a chemical compound that is used in water treatment and bleaching.

Chlorate and chlorite:  oxidants and reaction products of chlorine dioxide, a   primary drinking water disinfectant. Chlorite and chlorate can also be formed from hypochlorous acid in water, but chlorite is rapidly oxidized to chlorate. 

Dichlorvos: is an organophosphorus insecticide used primarily for controlling household pests and for protecting stored products from insects. It is no longer approved for use in some jurisdictions because of concerns over its acute toxicity.

Dicofol: an organochlorine acaricide registered for broad-spectrum contact, nonsystemic control of plant-eating mites in cotton, tea and a wide variety of fruit, vegetable and ornamental crops. Products containing dicofol are being phased out in the United States and are not approved in the EU.

Diquat: a nonselective herbicide that is used for weed control on several food crops, for residential weed control on lawns and ornamental plants and as an aquatic herbicide for the control of free-floating and submerged aquatic weeds.

Lead: a legacy from an earlier age, potential lead exposure can be through lead pipes and plumbing— whether from service laterals, privately owned lines, or home fixtures, fittings and solder. The major concern is if the drinking water is excessively corrosive so that it solubilizes lead from the pipe or fixtures.

MCPA: a phenoxyacetic acid herbicide that is found in various formulations. It is widely used against broadleaf weeds. All forms of MCPA will dissociate in water to the acid (anion) form. It is highly soluble in water and is biodegradable.

Perchlorate: is both a naturally occurring and synthetic anion that is sometimes found in water at microgram-per-liter levels resulting from contamination from perchlorate manufacturing or use, solar oxidation of precursors,  fertilizers containing natural deposits of perchlorate.



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