Lead in drinking water: what Canadian guidelines require and how testing works

Health Canada revised its Maximum Acceptable Concentration for lead in drinking water to 0.005 mg/L in 2019, cutting the previous guideline in half. For older buildings with lead solder or lead service lines, that revision changed what a passing result looks like. This article explains the sampling protocol and what to do with the numbers.

Why the sampling protocol matters as much as the analysis ¶

Lead in drinking water almost always comes from the plumbing, not the source water. That means the concentration at the tap depends heavily on how long water has been sitting in contact with lead-containing materials. A sample collected after the tap has been running for two minutes will typically show much lower lead than a sample collected after an overnight stagnation period.

Health Canada's guidance recommends a first-draw sample collected after at least six hours of stagnation, with no prior flushing. This is the sample most likely to capture lead released from service lines and internal plumbing. Some provincial programs also require a flushed sample for comparison. If you are collecting samples for a regulatory program, confirm the protocol with the program administrator before collection. The laboratory can only report what is in the bottle.

What the 0.005 mg/L guideline means in context ¶

The 0.005 mg/L MAC is a health-based value derived from a tolerable daily intake for the most sensitive population group, which is infants and young children. It is not a zero-risk threshold. It is the concentration at which Health Canada considers the risk to be acceptable for lifetime exposure. Results below the MAC do not mean lead is absent; they mean the concentration is below the level considered to require action.

For buildings constructed before 1990 in Ontario, lead solder was commonly used in copper plumbing until it was phased out under the Ontario Building Code. Buildings with original plumbing from that era are reasonable candidates for first-draw testing, particularly if they serve vulnerable populations.

Interpreting results and next steps ¶

A result above 0.005 mg/L in a first-draw sample warrants follow-up, but the appropriate response depends on the magnitude and the building type. For a single-family home, flushing the tap for two minutes before use is a short-term measure while longer-term options (filter installation, service line replacement) are evaluated. For a multi-unit building or a facility serving children, the response threshold is lower and the timeline for action is shorter.

The laboratory report will show the result in mg/L alongside the Health Canada MAC. If you need the result in a format suitable for a landlord disclosure or a municipal reporting program, note that requirement at intake and we will structure the report accordingly.

Lead testing is one of those cases where the collection protocol and the analysis are equally important. If you have questions about how to collect a valid first-draw sample from your building, contact us before you go to the tap.