Where does my tap water come from?

In the year 2000, the town of Walkerton in southwestern Ontario had E.coli bacteria in one of their drinking supply wells that resulted in the death of six people and over 2,000 residents becoming sick. The water supply became contaminated at a pumping well that was close to a farm where cattle manure (which contains E.coli) was used to fertilize crops. Heavy rains in May 2000 carried the bacteria into the ground and towards the nearby supply well. Inadequate chlorination led to the distribution of contaminated water to residents and within days, residents began getting sick, with outbreaks of gastroenteritis occurring in the community. The public inquiry that followed concluded that negligence (including falsification of reports, failure to report) as well as inadequate chlorination and the shallow depth of the water supply well (combined with its proximity to cattle manure) led to this tragedy.

As a result of the Walkerton tragedy. the provincial government in Ontario developed a framework to protect drinking water. This framework includes laws and regulations, drinking water standards, regular testing, licensing and training of operators, transparency and a focus on source-to-tap. Locally, source water protection plans include understanding the sources of drinking water and implementing plans for the protection of these and future sources of drinking water.

That’s a lot of preamble for this article but I want to stress the importance of understanding where our water comes from. I live in Kitchener-Waterloo (KW) where about 75% of the water supply comes from groundwater (the remaining 25% comes from the nearby Grand River). The Region of Waterloo, the local government in charge of water distribution, has over 100 water supply wells spread throughout the KW area.

Through some online digging, I learned that near me, the tap water is coming from the William Street pumping wells in uptown Waterloo. The William Street well field has been in operation since 1899 and is the first site of public groundwater use in the area.

When we talk about protection of our water resources, we need to consider two things: (1) water quality, and (2) water quantity. For groundwater resources, protecting water quality means identifying potential sources of contamination (gas stations, agricultural fertilizers, road salt, for example) that might get to the water supply. To aid in understanding this, computer models can be used to estimate from where water wells are getting water. Recent reports from consultants and the Region of Waterloo show that the William Street wells pump groundwater from an area that extends from the pumping wells towards the west. The figure below (reference here, page 94) shows a map that requires more explanation.

Towards the right (east) of the map, there are small green dots labelled W1C, W1B and W2. These are three pumping wells at the William Street well field. The coloured polygons around this well field represent well head protection areas (WHPAs) of different water travel times to the wells. The largest yellow area indicates the 25-year WHPA. In other words, all groundwater within this yellow zone is predicted to reach the William Street pumping wells within 25 years. The darker colours represent shorter groundwater travel times to the pumping wells (5, and 2 years). Urban planners make use of maps like this to help in decision making (e.g., what can be built where). The 2, 5, and 25 year zones are estimated to aid in protecting the water quality at the water wells.

But it’s a little more complex than that. When we want to protect the water quantity, we need to understand from where groundwater is coming beyond 25 years. The groundwater within this 25-year WHPA zone comes from somewhere. At some point in time, rain hit the ground and some of the rain seeped into the ground (water that enters the ground is called “recharge”) and moved slowly towards this 25-year zone. And where the rain entered the ground is not necessarily within this 25-year zone. Some of the groundwater in this zone entered the ground far from this area.

To look at this in more detail, the Region of Waterloo, through the use of numerical models, has mapped out recharge areas that contribute water to each supply well. The recharge water might take decades or even centuries to travel to the pumping wells. As an example, if one was to pave over a recharge area, water will be prevented from entering the ground. While this might not affect the water supply at a well in 5 or 25 years, it could have long-term consequences on water that is available for the water wells.

Remember, the William Street well field has been in operation since the 1890s. So these water supply wells have likely been pumping water from an area much larger than the 25-year zone shown in the map above.

So it makes sense to protect the recharge areas. The map below (reference here) shows areas (coloured orange) where recharge to the KW wells is estimated to occur¹. This orange area represents the interpreted regional recharge area for the municipal water supply wells in Kitchener-Waterloo, including the William Street wells, shown in the northeast of the map below. What's not shown is the groundwater travel times from the recharge area to the wells. However, we can infer that the time for groundwater to travel from the recharge area to the wells can be much higher than 25 years (based on the size of the WHPAs in the previous map).

If too much of the recharge area is altered, groundwater can be depleted. In addition, rather than recharging, rain water is often diverted to streams, which can increase the potential for flooding issues. The Region of Waterloo has studied these issues in considerable detail. However, developers continue to pressure the Region. A single, new development area might cover over a small area that affects a fraction of a percent of the recharge to a pumping well. However, the cumulative effect of many new developments over a recharge area will likely have an effect that may not be detected for years or decades into the future.

I will sum up this post by saying we need to understand where our water comes from and what is being done to protect our water sources. In my case, I know the Region of Waterloo is working hard to protect the water that comes out of my tap. However, I question whether or not the current provincial government has our best interests in mind².

1. Maps like this have been updated to reflect new data and understanding. As a consultant, I was involved in a project to update the regional recharge area for the Region of Waterloo in 2019, but I was unable to find that report online.

2. Here’s a link to a report from the Auditor General: https://www.auditor.on.ca/en/content/annualreports/arreports/en21/AR_LandUse_en21.pdf