Drinking Water in the NWT

Chemical and Physical Sampling


Alkalinity is an index of the buffering capacity of water. It is closely linked to hardness. For the most part, alkalinity is produced by anions or molecular species of weak acids, mainly hydroxide, bicarbonate and carbonate; other species such as borates, phosphates, silicates and organic acids may also contribute to a small degree. Alkalinity is expressed in terms of an equivalent quantity of calcium carbonate. As the alkalinity of most Canadian surface waters is due to the presence of carbonates and bicarbonates, their alkalinity is close to their hardness.


The maximum acceptable concentration (MAC) for lead in drinking water is 0.010 mg/L

Lead is a poison that can negatively affect the central nervous system. Pregnant women, infants and children up to 6 years of age are most vulnerable. Lead is present in tap water as a result of dissolution from natural sources or from old household plumbing systems containing lead in pipes, solder or household service connections. The amount of lead from the plumbing system that may be dissolved depends upon several factors, including the acidity (pH), water softness and standing time of the water.

Lead has not been used in drinking water distribution systems or in household plumbing since 1945. People living in older homes in particular, should run the water for a few minutes to clear out the water that has been sitting in the pipes before drinking it. Faucets should also be flushed before water samples are taken for testing. Lead is generally not a concern in the NWT, where there are few older houses or distribution systems.


Neither a health-based guideline (MAC) nor an aesthetic objective (AO) has been established for aluminum in drinking water. Aluminum is the most abundant metal on Earth – about 8% of the Earth’s crust. It is found in a variety of minerals. Aluminum is chiefly mined as bauxite, a mineral containing 40–60% aluminum oxide (alumina). Aluminum is also found as a normal constituent of soil, plants and animal tissues.

As a precaution, water treatment plants using aluminum-based coagulants should optimize their operations to reduce residual aluminum levels in treated water to the lowest extent possible. For plants using aluminum-based coagulants, recommended values are less than 0.1 mg/L total aluminum for conventional treatment plants and less than 0.2 mg/L total aluminum for other types of treatment systems (e.g., direct or in-line filtration plants, lime softening plants). These values are based on a 12-month running average of monthly samples.


The interim maximum acceptable concentration (IMAC) for arsenic in drinking water is 0.025 mg/L. Levels of arsenic in natural waters generally range between 0.001 and 0.002 mg/L.

Sources of arsenic in the air around us come from the burning of fossil fuels (especially coal), metal production, agricultural use and waste incineration. Arsenic is introduced into water through the dissolution of minerals and ores, from industrial effluents and from the atmosphere. Natural sources, such as arsenic-containing rock that dissolves, often contribute significantly to the arsenic content of drinking water and groundwater.


The maximum acceptable concentration (MAC) for barium in drinking water is 1.0 mg/L.

Barium is present as a trace element in both igneous and sedimentary rocks. Although it is not found free in nature, barium occurs in a number of compounds, most commonly barite (BaSO4) and, to a lesser extent, witherite (BaCO3). Barium is not considered a contaminant in the NWT.


The maximum acceptable concentration (MAC) of 0.005 mg/L for cadmium in drinking water was set based on health considerations.

Cadmium is a silvery-white, lustrous, but tarnishable metal that closely resembles zinc. It is soft and ductile and has a relatively high vapour pressure. Cadmium is not considered a contaminant of concern in the NWT.


The aesthetic objective (AO) for chloride in drinking water is 250 mg/L. At concentrations above the AO, chloride makes water, and drinks made from water, taste bad. It may also cause corrosion in the distribution system.

Chloride is widely distributed in nature, generally as sodium (NaCl) and potassium (KCl) salts. By far the greatest amount of chloride found in the environment is in the oceans. Chloride in drinking water sources can come from dissolving salt deposits, salting of highways to control ice and snow, effluents from chemical industries, oil well operations, sewage, irrigation drainage, refuse leachates, sea spray and seawater intrusion in coastal areas. Chloride is generally present at low concentrations in natural surface waters in Canada. Concentrations are normally less than 10 mg/L and often less than 1 mg/L.


The maximum allowable concentration (MAC) of 0.05mg/L for chromium in drinking water was set based on health considerations.

Trivalent chromium, the most common natural state of chromium, is essential in humans and animals for efficient lipid, glucose and protein metabolism. It is considered to be non-toxic. However, if it is present in raw water, it may be oxidized to hexavalent chromium during chlorination. Concentrations of total chromium in drinking water are usually well below the MAC. Chromium is not considered a contaminant of concern in the NWT.


The aesthetic objective (AO) for colour is 15 TCU (true colour units). Colour is not a health-related parameter.

Colour in drinking water may be due to the presence of coloured organic substances, metals such as iron, manganese and copper or highly coloured industrial wastes. Although presence of colour in drinking water is not directly related to health, experience has shown that consumers may turn to alternative, possibly unsafe, sources, if their drinking water is highly coloured.


The aesthetic objective (AO) for copper in drinking water is 1.0 mg/L. This was set to ensure the water tastes okay and to minimize staining of laundry and plumbing fixtures.

Copper is an essential element in human metabolism, and deficiencies result in a variety of clinical disorders, including nutritional anemia in infants. Although large doses of copper may result in adverse health effects, the levels at which this occurs are much higher than the aesthetic objective (AO). Copper occurs in nature as a metal and in minerals. Copper is not a contaminant of concern in the NWT.


Cyanide is toxic to humans, and the maximum acceptable concentration (MAC) for free cyanide in drinking water is 0.2 mg/L.

Cyanides may be released into the aquatic environment through waste effluents from various industries such as gold mining. Representative data suggest that Canadian drinking water has very low concentrations of cyanide. Contamination through industrial spillage or transport accidents could result in high cyanide levels in raw water supplies. Cyanide is not considered a contaminant of concern in the NWT.


Water sources in the NWT typically have naturally occurring fluoride levels between 0.1 and 0.3 mg/L. Based on the recommendation of Health Canada’s Chief Dental Officer, the NWT Chief Public Health Officer has determined that the optimal concentration of fluoride in drinking water for dental health benefits should be 0.7 mg/L.  Canadian Drinking Water Quality Guidelines have set a maximum acceptable concentration of 1.5 mg/L  of fluoride in drinking water.

 The addition of fluoride into drinking water remains one of the most cost-effective and accessible interventions community leaders can take to improve oral health in their communities. More information is available on the Health Canada website:


Most communities in the NWT do not add or remove fluoride. However, presently (2015) the communities of Inuvik, Fort Smith and Yellowknife boost water fluoride levels for dental health. Communities that do add fluoride monitor levels with daily samples.

For more information on how your community manages fluoride in drinking water, please contact your community government or the regional Environmental Health Officer.


The aesthetic objective (AO) for iron in drinking water is 0.3 mg/L. At concentrations above the AO, iron can make water taste bad and can cause staining of laundry and plumbing fixtures.

Iron is an essential element in human nutrition, and deficiencies can result in impaired mental development in children, reduced work performance in adults and, in severe cases, anemia or impaired oxygen delivery. Iron is the fourth most abundant element in the earth’s crust and the most abundant heavy metal. It is present in the environment mainly as Fe(II) or Fe(III). The concentrations of iron in Canadian surface waters are generally below 10 mg/L. Iron is generally present in surface waters as salts containing Fe(III) when the pH is above 7. Most of those salts are insoluble and settle out or are adsorbed onto surfaces Therefore, the concentration of iron in well-aerated waters is seldom high. Under reducing conditions, which may exist in some groundwaters, lakes or reservoirs, and in the absence of sulphide and carbonate, high concentrations of soluble Fe(II) may be found. The presence of iron in natural waters can be attributed to the weathering of rocks and minerals, acidic mine water drainage, landfill leachates, sewage effluents and iron-related industries.


The aesthetic objective (AO) for manganese in drinking water is 0.05 mg/L.

Manganese in drinking water supplies can cause a number of problems. At concentrations above 0.15 mg/L, manganese stains plumbing fixtures and laundry and produces undesirable taste in drinks. Manganese may cause microbial growths in the distribution system. Even at concentrations below 0.05 mg/L, manganese may form black coatings on water distribution pipes. The element manganese is present in over 100 common salts and mineral complexes that are widely distributed in rocks, in soils and on the floors of lakes and oceans. Manganese is most often present as the dioxide, carbonate or silicates. Manganese is most often a concern for systems that use a groundwater source.


Mercury is a toxic element and provides no benefit to humans. The maximum acceptable concentration (MAC) for mercury in drinking water is 0.001 mg/L.

Mercury is a concern because organic mercury accumulates in fish. Elevated mercury levels have been found in freshwater fish taken from areas with suspected mercury contamination and frequently render the fish unsafe to eat. Long-term daily intake of approximately 0.25 mg of mercury as methyl mercury has caused the onset of neurological symptoms; however, even in heavily polluted Canadian waters, mercury concentrations rarely exceed 0.03 mg/L. The MAC for mercury, therefore, provides a considerable margin of safety. Mercury levels in both surface water and tap water are generally well below the maximum acceptable concentration. Mercury is not considered a contaminant of concern in the NWT.


The maximum acceptable concentration (MAC) for nitrate in drinking water is 45 mg/L. In cases where nitrite is measured separately from nitrate, the concentration of nitrite should not exceed 3.2 mg/L.

The most commonly reported toxic effect of nitrate-contaminated drinking water is methaemoglobinaemia, which results in reduced oxygen transfer to body tissues. Infants up to 3 months of age are most vunerable. Nitrate (NO3‾ ) and nitrite (NO2‾ ) are naturally occurring ions that are found everywhere in the environment.

Both are products of the oxidation of nitrogen (which comprises roughly 78% of the atmosphere) by micro-organisms in plants, soil or water and, to a lesser extent, by electrical discharges such as lightning. Nitrate is the more stable form of oxidized nitrogen but can be reduced by microbial action to nitrite, which is moderately reactive chemically.

Sources of nitrates in water (particularly groundwater) include decaying plant or animal material, agricultural fertilizers, manure, domestic sewage, or geological formations containing soluble nitrogen compounds. Nitrate is not considered a contaminant of concern in the NWT, as there is very little commercial agriculture.


An acceptable range for drinking water pH is from 6.5 to 8.5. Water with a pH below 6.5 is considered acidic and may cause corrosion. Water with a pH above 8.5 is considered basic, and may result in incrustation and scaling problems. As pH increases, there is a progressive decrease in the efficiency of the chlorine disinfection process.


Selenium occurs naturally from erosion and weathering of rocks and soils, due to release from coal ash from coal-fired power plants, and from mining and refining of copper and other metals. Selenium can also be found in non-leaded brass alloy where it is added to replace lead. The maximum acceptable concentration (MAC) for selenium in drinking water is 0.05 mg/L.

Selenium is an essential nutrient. The MAC is based on chronic selenosis symptoms in humans following exposure to high levels. Other symptoms include hair loss, tooth decay, weakened nails and nervous system disturbances at extremely high levels of exposure. Most exposure is from food; there is little information on the toxicity of selenium from drinking water.


The aesthetic objective (AO) for sodium in drinking water is 200 mg/L. Drinking water generally tastes bad at sodium concentrations above the AO. Sodium is not considered a toxic element. Adults normally consume up to 5 grams of sodium a day. Although the average intake of sodium from drinking water is only a small fraction of that consumed in a normal diet, the intake from this source could be significant for people suffering from hypertension or congestive heart failure who may require a sodium-restricted diet.

Sodium is the most abundant of the alkali elements and makes up 2.6% of the Earth’s crust. Sodium compounds are widely distributed in nature. Sodium is a soft, silvery-white, highly reactive metal. It is never found in nature in the uncombined state and has a strong tendency to exist in the ionic form. In biological systems and even in solids such as sodium chloride, sodium remains distinctly separate as the sodium ion.


The aesthetic objective (AO) for sulphate in drinking water is 500 mg/L, based on taste. Because of the possibility of adverse physiological effects at higher concentrations, health authorities should be notified if drinking water sulphate concentrations exceed 500 mg/L.

Sulphur is a non-metallic element. Sulphur, principally in the form of sulphuric acid, is one of the most widely used chemicals in industrialized society. Most sulphur is converted into sulphuric acid.

Sulphates or sulphuric acid products are also used in the manufacture of numerous chemicals, dyes, glass, paper, soaps, textiles, fungicides, insecticides, astringents and emetics. They are also used in the mining, pulping, metal and plating industries. Aluminum sulphate (alum) is used as a sedimentation agent in the treatment of drinking water, and copper sulphate has been used for the control of blue-green algae in both raw water and public water supplies in the United States. Sulphate is not considered a contaminant of concern in the NWT.

Total Dissolved Solids (TDS)

An aesthetic objective (AO) for total dissolved solids (TDS) in drinking water is 500 mg/L. At higher levels, excessive hardness, poor taste, mineral deposition and corrosion may occur. At low levels, however, TDS contributes to the good taste of water.

Total dissolved solids (TDS) include inorganic salts and small amounts of organic matter that are dissolved in water. The principal constituents are usually the cations calcium, magnesium, sodium and potassium and the anions carbonate, bicarbonate, chloride, sulphate and, particularly in groundwater, nitrate (from agricultural use). Total dissolved solids in water supplies originate from natural sources, sewage, urban and agricultural runoff and industrial wastewater.

Total Hardness

Although hardness may have significant aesthetic effects, a maximum acceptable level has not been established because public acceptance of hardness may vary considerably according to the local conditions. Water supplies with a hardness greater than 200 mg/L are considered poor, but have been tolerated by consumers; those in excess of 500 mg/L are unacceptable for most domestic purposes. Higher levels are generally associated with groundwater sources.

Water hardness is a traditional measure of the capacity of water to react with soap. Hard water requires a considerable amount of soap to produce a lather, and it also leads to scaling of hot water pipes, boilers and other household appliances. Water hardness is caused by dissolved polyvalent metallic ions. In fresh waters, the principal hardness-causing ions are calcium and magnesium; strontium, iron, barium and manganese ions also contribute.


Turbidity is a measure of the relative clarity or cloudiness of water. Turbidity in water is caused by suspended and colloidal matter, such as clay, silt, finely divided organic and inorganic matter, and plankton and other microscopic organisms. Turbidity is not a direct measure of particles suspended in the water. It is, rather, a measure of the scattering effect that such particles have on light. A beam of light remains relatively undisturbed when it shines through absolutely pure water, but if there are particles in the water, the light will bounce off the particles and scatter in different directions.

Turbidity is considered a health-related parameter because the particles can shelter bacteria from chlorine disinfection and act as a food source for micro-organisms. Water with high turbidity may increase the amount of chlorine required for disinfection and the possibility of water-borne illness.


The interim maximum acceptable concentration (IMAC) for uranium in drinking water is 0.02 mg/L.

Uranium is present in water supplies as a result of leaching from natural deposits, release from mill tailings, emissions from the nuclear industry, and the combustion of coal and other fuels. Phosphate fertilizers may also contribute to the uranium content of groundwater. Uranium is not considered to be a contaminant of concern in the NWT.


The aesthetic objective (AO) for zinc is 5.0 mg/L. Zinc is an essential element is generally considered to be non-toxic. Drinking water is not considered an important nutritional source of this element. Water containing zinc at concentrations above 5.0 mg/L tends to be opalescent, develops a greasy film when boiled, and has an undesirable astringent taste.

Zinc is an abundant element. The most common zinc mineral is sphalerite (ZnS), which is often associated wth the sulphides of other metallic elements, such as lead, copper, cadmium, and iron. Zinc is not considered to be a contaminant of concern in the Northwest Territories.

Total Organic Carbon (TOC)

Total Organic Carbon is a measure of the organic compounds in the water. Organic compounds may come from plants or animals, from biofilms or bacteria in the water system, or from products such as petroleum or plastic. Organics are monitored due to their potential to react with chlorine to form disinfection by-products such as trihalomethanes. Water systems using sources that are high in organics generally have treatment systems that are designed to remove the organics prior to adding chlorine.

Dissolved Organic Carbon (DOC)

Dissolved Organic Carbon is a measure of the dissolved portion of the organic compounds in the water. Organic compounds may come from plants or animals, from biofilms or bacteria in the water system, or from products such as petroleum or plastic. Organics are monitored due to their potential to react with chlorine to form disinfection by-products such as trihalomethanes. Water systems using sources that are high in organics generally have treatment systems that are designed to remove the organics prior to adding chlorine.

Total Suspended Solids (TSS)

Total suspended solids (TSS) are monitored for both health and aesthetic reasons. Organic contaminants and heavy metals are adsorbed on particulates, and this suspended matter can shield microorganisms from disinfectants and can lead to odour problems.

Trihalomethanes (THMs)

The interim maximum acceptable concentration (IMAC) for total trihalomethanes (THMs) in drinking water is 0.1mg/L. THMs are the by-products that result when chlorine is mixed with organic particles. If raw water has a lot of organic material, THMs can be produced during disinfection. Drinking water with a lot of THMs over a very long period of time may be linked to cancer, but drinking water that is not disinfected with chlorine is a much bigger health risk.