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Drinking sufficient water is essential for health, including digestion and elimination of water-soluble wastes and toxic substances.

High quality drinking water, as well as water for sanitation, is of utmost importance and is a human right.

Water Quality

Non-binding water quality (and other) guidelines are published by the Canadian Council of Ministers of the Environment (CCME) and may be applied by provincial and local governments. Canada’s standards are unfortunately reported to be lax and unenforceable compared with international best practices.

Municipal drinking water is usually chlorinated to kill germs, but reactions with organic content (such as rotting vegetation or animal wastes) in the water can create carcinogenic chemicals called disinfection byproducts (DBPs). DBPs are ingested and linked to bladder and some gastrointestinal cancers, according to a 2021 review by the US National Institutes of Health. DBPs also evaporate quickly, so a substantial dose can be inhaled during a hot shower, compared with much less in a drink of water. If you boil water or let it sit, many DBPs will off-gas. A glass jug of water left in the fridge will have lower levels of DBPs the next day.

Different concerns may come with private wells. Health departments generally process water samples for bacteria. You should check with your public health department for water testing recommendations for naturally occurring chemicals (e.g. arsenic or uranium) or environmental contaminants that may affect your water (e.g. from emergency training, old industries or dump sites).

Lead from old pipes and fittings is still leaching into drinking water in too many homes. Drink water only from the cold water tap after letting the water run until it is cold, especially first thing in the morning or after time away from home. Consider replacing plumbing, and work to have your municipality replace old lead water supply pipes. Drinks should never be stored in leaded glass (crystal) containers. Beside increased cancer risks, even low levels of lead harm children’s developing brains and organs. Lead is stored in bones, and continues to cause diverse harms at all ages.

A wide range of water filters are available. Many people use simple activated carbon filters, such as Brita pitchers and tap filters, which may remove some DBPs and lead. Reverse osmosis and activated carbon may be needed to remove a broader range of chemicals. Do your research, and be vigilant with maintenance and filter replacement.

Bottled water

Bottled water is not regulated as stringently as tap water, since it is treated as a food product and normal water testing is not required. This leads many public health bodies to encourage drinking water from the tap. Besides, there is an enormous environmental footprint of the oil, manufacturing and transportation up front, plus disposal of billions of plastic bottles. Glass or stainless steel reusable drinking water containers are much better options. Polycarbonate hard, clear plastic breaks down to release bisphenol-A, an endocrine disruptor. Many “bisphenol-A free” plastic substitutes (e.g. bisphenol-S) are now also recognized as endocrine disruptors. Soft plastics may leach other substances such as phthalate plasticizers (added to increase flexibility of the plastic). If you must use plastic, remember that the most readily recyclable plastic containers and bags are less likely to leach toxic chemicals, (see plastics information).

Scientific fine print: Halogens – fluoride, chloride and iodide

The term “halogens” refers to a family of chemicals including fluorine, chlorine, bromine and iodine. They are commonly in salts, in safer chemical forms – fluoride, chloride, bromide and iodide.

When halogens are incorporated in organic chemicals, the substances are more persistent, and have remarkable characteristics as water and oil repellents (e.g., coatings for cookware and textiles), flame retardants, or more potent pesticides. These families of chemicals can contaminate drinking water, causing a range of ill health effects.

Chloride is the predominant halogen in the body. It is in table salt (sodium chloride) and is essential to maintain bodily fluids and functions. Not to be confused, the chlorine chemicals in bleach and for water treatment are very reactive and very different from salt.

Iodine is an essential component of thyroid hormone. Iodide salt may also be given to people to minimize absorption of radioactive iodine used in medical imaging or even following nuclear disasters, to prevent thyroid cancer. In efforts to minimize health effects of iodine deficiencies, it is added to flour and to table salt.

The lightest halogen, fluorine, is more contentious. Whether fluoride is truly an essential nutrient is not certain. Unlike iodide and chloride, health effects from insufficient fluoride have not been observed. Fluoride is common in our environment, water and diet, and at high enough levels it can interact with essential halogens, particularly iodide, indirectly impacting thyroid activity. Fluoride is chiefly bound in bone and teeth, and at low levels can contribute to their hardness. Higher levels cause weakening of bones and tooth structure, most obvious as mottling of teeth or dental fluorosis.

Fluoride-containing additives sometimes used in drinking water in an attempt to prevent dental caries may be byproducts of aluminum or fertilizer production. This occurs in a steadily decreasing number of jurisdictions, principally in North America. In fact, addition of fluoride to drinking water cannot be credited with decreases in decayed, missing or filled teeth (DMFT), as improvements in oral hygiene in the modern era caused reductions in caries in areas both with and without fluoride added to drinking water (see Figure). The one and only study that carefully characterized early life exposure to fluoride in drinking water found increased risk of osteosarcoma in adolescent males who had been exposed to higher levels of fluoride in drinking water during their childhood. More recent studies in China and Canada found that exposure to fluoride in utero, and to a lesser extent in early childhood, reduces IQ .

Image credit: Fluoride Action Network (

Prevent Cancer Now opposes the addition of fluoride to drinking water, as it offers no discernible benefit and poses risk of cancer and lower IQ with exposures early in life. As well, other toxins may be contained in the industrial wastes that are used as fluoride-containing additives.

The big picture for water

Drinking water may naturally contain such carcinogens as arsenic, heavy metals or radioactive chemicals. Water may also be contaminated by previous and ongoing activities such as agriculture, mining for minerals or bitumen, hydraulic fracturing for petrochemicals (“fracking”), industrial activities, waste disposal or other land “uses.” Ground- and surface-water may contain fertilizers and pesticides, toxic minerals or petrochemicals, or a broad range of other industrial toxicants. Your public health department should know of local risks, and it is also good to know the history of the land before moving to a new location.

Be careful of what goes down the drain, because wastewater and downstream drinking water treatment plants are not designed to remove many modern chemicals, including pesticides, pharmaceuticals and ingredients in personal care products and cleaners.

Protect source water by:

  • reducing wastes entering waterways from runoff, septic tanks or industries;
  • keeping livestock out of streams; and
  • maintaining vegetated shorelines and wetlands – nature’s filters.

This minimizes organic and nitrogen-containing materials entering the drinking water treatment plant and naturally minimizes chlorination byproducts.

Increasing populations, intensive agriculture, industrial expansion, urban sprawl and climate change are all making clean drinking water supplies more precarious. Glaciers are melting, underground reservoirs are being depleted and becoming salty, and natural features that clean water and water sources are being impacted by development, invasive species and severe weather. Through the lens of water, it is clear that tackling broader environmental issues also impacts cancer prevention.