Buying a House with a Well and Septic System (CMHC)

In rural areas, many homes do not have connections to municipal water and sewer lines. Homeowners rely upon privately owned or communal (shared) wells as their drinking water source, and individual septic systems to treat and discharge their wastewater. Homeowners must ensure that their well water is safe to drink, and that their well and septic system are properly maintained. A malfunctioning well or septic system can pose a health risk to your family and neighbours, and can be expensive to repair or replace. It is therefore important to conduct a detailed inspection of both the well and septic system prior to purchasing a home. This document will describe how wells and septic systems function and how to inspect them.

Wells

When you are purchasing a home with a private water supply (a well), there are three key items to consider:

  • well system
  • water quantity
  • water quality

Well Systems

There are three common types of wells: dug, bored and drilled.

Common features of well systems include:

Casing – structure around the well hole, which keeps it from collapsing. It could be a steel casing, concrete rings or an open hole in bedrock.

Inlet – allows water to enter the well from the bottom. There might be a screen at the inlet to prevent fine particles from entering the well and a foot-valve (check valve) to maintain system prime and pressure.

Pumping system – includes pump, piping and necessary electrical connections to pump water from the well into the house, and a pressure tank to maintain constant water pressure in the house. Submersible pumps are usually used in drilled wells, while shallow wells usually use centrifugal pumps, which are located out of the well, most likely in the basement or in a pump house.

Surface protection – prevents surface water and contaminants from entering the well. Includes: watertight seal placed around the casing (annular seal), well cap 0.3–0.4 m (12-16 in.) above the ground, and mounded earth around the top of the well casing to divert rainwater.

Water Quantity

Wells draw water from aquifers, which are zones of saturated permeable soil or rock. Some types of soil make for good aquifers, such as gravel and fractured bedrock that can support high water pumping rates, while other types of soil make for poor aquifers, such as silty sand and clay that cannot support high water pumping rates.

Wells can run dry for the following reasons:

  • The pumping rate is higher than the groundwater recharge rate.
  • The water table (level of saturated water in the soil) has dropped to below the pump suction or inlet.
  • The well screen has become plugged by fine sand, chemical precipitation, bacterial fouling or corrosion.
  • If a well vent becomes blocked, a negative pressure may occur (in the well) during draw down and reduce or stop the pump from drawing water.

If there is a water supply problem, a licensed well contractor should be consulted. Solutions may include: water conservation in the home, digging a deeper well, unplugging a fouled well screen or replacing a corroded well casing or screen. The cost of fixing the problem should be considered when negotiating the sale price for the home.

There are three sources of information to help determine if a well can produce a sufficient quantity of water:

  • local knowledge
  • well record
  • water recovery test

Water Quality

The quality of the well water is very important. Poor water quality can lead to health problems, unpleasant taste and odour, and costly treatment systems and/or the costly use of bottled water. Well water can be contaminated with bacteria and chemicals. Common sources of contamination include infiltration from septic systems, manure runoff, pet waste, or road chemicals as well as dissolved chemicals naturally present in the groundwater such as calcium, sulphur, chloride or iron.

Septic Systems

The septic system accepts wastewater from the home (sinks, shower, toilets, dishwasher, washing machine), treats the wastewater and returns the treated effluent to the groundwater. A conventional septic system is comprised of two components: a septic tank and a leaching bed.

Septic Tank

A septic tank is a buried, watertight container, which accepts wastewater from your house (see Figure 4). Septic tanks can be made from concrete, polyethylene or fibreglass and in the past were sometimes made from steel (if the property has a steel tank, it is likely rusted through and needs replacing). Older tanks may be smaller than those found today (the minimum current size in Ontario is 3,600 L (952 US gal). Current tanks have two compartments, while older tanks may only have one compartment. Solids settle to the bottom of the tank to form a sludge layer, and oil and grease float to the top to form a scum layer. The tank should be pumped out every three to five years or when 1/3 of the tank volume is filled with solids (measured by a service provider such as a pumper). Some municipalities require that septic tanks be pumped out more frequently. Bacteria, which are naturally present in the tank, work to break down the sewage over time.

Leaching Bed

The wastewater exits the septic tank into the leaching bed—a system of perforated pipes in gravel trenches on a bed of unsaturated soil (minimum 0.9 m/3 ft.—see Figure 5). The wastewater percolates through the soil where microbes in the soil remove additional harmful bacteria, viruses and nutrients before returning the treated effluent to the groundwater. In cases where there is more than 0.9 m (3 ft.) of unsaturated soil from the high water table or bedrock, a conventional system is used, where the network of perforated drainage piping is installed either directly in the native soil or in imported sand if the native soil is not appropriate for treatment. In cases where the groundwater or bedrock is close to the surface, the leaching bed must be raised 0.9 m (3 ft.) above the high water table or bedrock. This is called a raised bed system.

Source: Canada Mortgage and Housing Corporation