Where does the water come from that we get from our taps?

Sunday, May 24, 1998

In a number of communities, water comes from the ground. This unlike many other communities where water comes from lakes or rivers. Groundwater accounts for only about six percent of the total water used in Ontario, over 2.8 million people, 23 percent of Ontario's population rely on it as a source of potable water.

How does the water get into the ground?

water cycle

When it rains, water runs along the ground surface and into storm sewers or streams, and some water seeps into the ground. Of this water, some is used by plants, the rest seeps downward, becoming groundwater. The groundwater flows underground and eventually emerges into streams or lakes. Groundwater is part of the hydrologic cycle (water cycle), which includes clouds, rain, snow, streams, lakes and oceans.

How is water stored in the ground?

The ground consists of various earth materials. The pores between the soil grains provide space for water to seep into. In soils such as sand or gravel, the pores are large and water can move through easily; such soils make up what is known as aquifers. In other soils, such as clay, the pores are small and water can move through only very slowly; such materials make up what we call aquitards. The level to which groundwater rises underground is called the water table. In many areas several layers of acquifers and aquitards are found underground. Since the soil varies from place to place, the amount of water that seeps into the ground varies.

Where does the water go?

In some places the water seeping into the ground reaches an acquifer. The areas where this happens are called recharge areas. These are usually high-lying areas that look dry. Areas where the groundwater seeps out of the ground are called discharge areas. These are wetlands, streams, or lakes. The area that contributes its groundwater to a particular stream or lake is called a watershed. The ground water system in Ontario consists of many local watersheds. All streams and wetlands depend on groundwater, and groundwater, in turn; depends on a steady recharge. If the recharge is reduced (for example by paving over a recharge area to make a parking lot), a stream or wetland may dry up.

How does the water get out of the ground and into our taps?

Groundwater is pumped from aquifers to provide water. Municipalities are the largest users of groundwater in Ontario followed by agricultural and industrial activities.

What is the quality of our groundwater?

The aquifers that provide our tap water yield water of very high quality. Some of the bottled water that we can buy in stores comes from aquifers in the province. For the most part, the aquifers are protected by overlying aquifers which prevent pollutants from reaching the aquifers. Now, more of our land area has become urbanized, chlorine disinfectant is added as a precaution. The chlorine added to the drinking water varies from municipality to municipality (try a glass of tap water next time you visit Ottawa, Toronto, Waterloo or London.)

How can the groundwater get polluted?

Pollutants enter the groundwater from many sources, such as septic systems, fields, landfill sites, chemical spills, or industrial waste ponds. In Elmira, toxic chemicals got into the ground from a leaking liquid waste pond. Shallow aquifers (those that lie close to the ground surface) in farming areas can get polluted easily. Most of the aquifers that supply drinking water are deeper aquifers that are protected by overlying aquitards. However, in some areas the protected layer is absent; these are the recharge areas that supply the water that keeps the water cycle going. Solvents, the kind that we use to dry-clean our clothes, can dissolve in groundwater when spilled and are very toxic. A leaking oil tank or litre of spilled engine oil can also put an aquifer at risk. Septic sewage systems, used in outlying areas where city sewers do not reach, pose a danger to the groundwater if they happen to be located in a recharge area. This is also why in most developed countries of the world, recharge areas are designated as groundwater protection zones.

Where are our aquifers and recharge areas?

We don't know exactly where our aquifers and recharge areas are and how far they extend. Unlike wetlands, we cannot easily see them. To find out, exploration must be done by drilling test holes into the ground and by measuring how much water can be pumped out. From this information, groundwater professions, called hydrogeologist, tell us the story of the groundwater system. It takes several years to do the job properly, because many holes must be drilled and thousands of bits of data must be analyzed.

Can pollution from one part of the region travel to other parts?

Pollutants spread and disperse in an aquifer, but they do not travel from one watershed to another. This is one of the strengths of our groundwater system. A part of it may get polluted but never the whole system. Overall, most of our aquifer system is still free of harmful pollution.

Can lawn chemicals cause a problem for the groundwater?

They can. Whether they will, depends on many factors. Different chemicals behave differently in the ground. Some pesticides biodegrade, they are eaten by soil bacteria, some attach themselves to the soil grains and remain more or less in place, while some are carried along by the groundwater. Most fertilizers (if applied in excess of what plants can use) are readily carried and will eventually discharge into streams or lakes. They end up in wells if we are not careful. The nitrate found in fertilizers can be harmful to unborn children. Fertilizers are a problem in farm areas. When you see a stream with algae in it, you know fields in the watershed have likely had too much fertilizer. Pesticides are less mobile.

What can be done if the groundwater gets polluted?

First, the source of the pollutant must be eliminated. Second, the polluted part of the aquifer must be cleared up. Once an aquifer is polluted, the cleanup can be expensive since only a tiny amount of toxic chemical can pollute an aquifer. Methods for the remediation (clean-up) of aquifers are being developed. Sometimes a polluted aquifer cannot be cleaned up completely and an alternative water source must be found, but this is also expensive, and the polluted aquifer may continue to discharge pollutants into streams and lakes. Surface water sources are not good alternatives as far as quality is concerned because most surface water in populated areas carry sizable pollution loads. The best way by far is to keep pollution from happening in the first place.

Has all this been known for a long time?

Some of it has, some not. Hydrogeology (groundwater science) is a young and growing science, and new things are learned every day.

How groundwater flows in the ground has been understood for quite a while. The reason we are starting to define our aquifers and recharge areas is that water was always plentiful, so there was no need to spend money on exploration. Now there is. Large gaps exist in our knowledge of how chemicals behave in the ground. (There are about 70,000 chemicals in use in the world today). Mostly, their behaviour depends on the conditions that exist in soil. The picture becomes more complicated when chemicals interact with each other in the soil and make up new chemicals. Much is being learned about how aquifers can be cleaned up. But more needs to be learned.

What can we do for our groundwater?

Environmental pollution is increasing everywhere in the world. But we must remember that what we put on the ground may reach the groundwater in some way. To help keep our groundwater clean, it is wise to avoid using toxic chemicals that might cause harm to the environment and the groundwater. The water we have now is the best water we will ever have. Let us use and manage it responsibly.