Drinking water sources and treatment

Public Health recommends that residents living in private dwellings that are not connected to municipal water test their drinking water at least 3 times per year, preferably in the spring, summer, and fall.

Drinking water sources

Residents living in private dwellings can obtain their personal drinking water from different water sources such as:

Surface water source

Surface water is any source of water that is open to the atmosphere and is subject to runoff from the land. This includes lakes, streams, rivers, ponds and springs. Because these sources are open to the environment and subject to runoff, it is likely that the water will contain micro-organisms, such as bacteria, viruses, and parasites that can cause illness.

Public Health Sudbury & Districts does not recommend that surface water be consumed unless it is treated through proper filtration and a disinfection system.

Drilled well

A drilled well consists of a hole bored into the ground, with the upper part lined with casing. The casing protects the groundwater source and provides a housing for the pumping mechanism and for the pipe that moves the water from the pump to the surface. Most drilled wells reach deep aquifers; therefore, they have a lower risk of contamination and a temperature. They are, however, more vulnerable to deep aquifer contaminants (for example, salt) and can have poorer natural water quality.

Dug well

A dug well is a hole in the ground dug by shovel or backhoe. A dug well is excavated below the groundwater table until incoming water exceeds the digger’s bailing rate. The well is cased with concrete casing to prevent collapse and then covered with a concrete cap. Dug wells are not deep, typically, reaching only 3 to 9 metres below ground. Being shallow, dug wells have a higher risk of contamination.

Well point

A well point, also called a sand point or driven point well is a small diameter well made with steel pipes that are threaded together and a well screen at the end which is usually 0.6 to 0.9 metres long. The screen allows groundwater to flow into the well while keeping the surrounding sand out. Because these wells access a shallow water table, they tend to have limited yield and possible water shortages in dry periods. Well points are also more vulnerable to near-surface contamination.

Drinking water treatment devices

A municipal water supply requires no additional treatment at the tap for health-related contaminants. This water supply has been treated to meet the standards for quality and purity required in the Ontario Drinking Water Standards (e-Laws Ontario).

There are many manufacturers and sellers of home water treatment devices. Some of these devices disinfect the water and others remove chemicals to render the water more aesthetically pleasing. Devices that improve aesthetics and chemicals in drinking water may be required to allow certain disinfection devices to function optimally.

Disinfecting devices

Disinfection is a physical or chemical process in which pathogenic micro-organisms are deactivated or killed. These include the following:


Ultraviolet (UV) light treatment can be used to destroy harmful micro-organisms without the addition of chemicals to your water. The ultra-violet energy attacks the genetic core of harmful microorganisms and rearranges the DNA/RNA, eliminating the micro-organism’s ability to reproduce. Since the microorganisms are not able to reproduce, they will not be able to cause disease.

This treatment device needs filtration prior to the water entering the UV light to remove particles and natural chemicals that give water colour or increase the water’s hardness. Filtration is also needed to remove microbes embedded in dirt particles. Proper filtration will ensure the effectiveness of the UV light treatment.

In most cases, a UV light treatment device is accompanied with a very fine filter, usually a 5-micron pre-filter. It may slow water flow. Regular maintenance is required to ensure that the UV lamp is kept clean.


Drinking water chlorination kills bacteria and viruses and other microbes. It also removes some forms of iron if the water is filtered after chlorination. Water chlorination is effective in killing disease-causing micro-organisms.

This treatment device needs filtration to remove microbes shielded or embedded in dirt particles, including parasites. It is important to handle chlorine carefully and to test chlorine levels. Maintenance of the dosing pump is required.


Ozonation kills most microbes but not cryptosporidium. It can remove organic compounds, including pesticides. Ozonation can also be used in combination with activated carbon filters. This treatment involves ozone being bubbled through the water, breaking down some parasites, all bacteria, and other harmful organic substances.

This system needs filtration to remove microbes embedded in dirt particles including parasites. This treatment device varies in effectiveness depending on application and manufacturer.

Reverse Osmosis

Reverse osmosis is a treatment system that removes nitrates, sulphate, hardness, most microbes, dirt particles and small amounts of some pesticides. This system uses a semi-permeable membrane where an applied pressure is used to overcome osmotic pressure.

This treatment system requires pre-filtration and softening of hard water. Lack of filtration can result in plugged membranes.

Aesthetic and chemical improvements devices

There are several devices that can remove chemicals in the drinking water and enhance its quality. These treatment devices do not kill or inactivate harmful bacteria, viruses, and parasites. These devices can soften the water and remove unpleasant taste and odours. These devices include the following:


Water softeners are used to reduce hardness that produces lime deposits on dish-washed items and gives a starched effect on laundry. This system removes calcium, magnesium, and certain other metal cations in hard water. The resulting soft water is compatible with soap and extends the lifetime of plumbing.

This system is not suitable for removing microbes or most chemicals and increased sodium concentration in treated water. Periodic replacement of softener salt and disposal of concentrated salty water are necessary.


Filters rely on small pore size of material to filter dirt, debris, and some bacteria out of water. Ceramic candle filters remove bacteria and parasites, but not viruses. Specifically rated filters should be used to remove very small particles.

Filters should not be used without further treatment. They usually need chlorination or UV light disinfection to remove and inactivate all bacteria, viruses, and parasites. Regular maintenance and replacement for proper operation are required.

Activated carbon contactors

These devices remove small amounts of some chemicals and are typically used for removing tastes and odours and reducing trace levels of organic chemicals.

These devices are not suitable for removing minerals or large volumes of chemicals. They must be replaced regularly, and it can be difficult to know when contactors are exhausted. These devices can become a dangerous source of bacteria, and cause taste and/or odour problems if not properly maintained.

Home water treatment device

If you have questions about a home water treatment device, please review the Ministry of Environment Conservation and Parks (MECP) best management practices manual online, for owners of drinking water wells. The Ministry also has information for wells on your property for residential drinking water well owners for the proper location, construction, maintenance, and abandonment of a well.

If you have further questions, please call Public Health Sudbury & Districts at 705.522.9200, ext. 464 (toll-free 1.866.522.9200) to speak with a public health inspector.

This item was last modified on May 24, 2022