Lead Levels in Drinking Water

Recently, there have been serious concerns raised about lead levels in the water supply for Flint, Michigan.  Lead concentrations in the range of 30 ppb (parts per billion) have been reported for the Flint water system.  These levels are well above the standard for lead in drinking water which has been established in Canada at 10 ppb (equivalent to 10 µg/L) or less as a safe level for human consumption.  Average levels in City of Ottawa’s water supply are as follows:  0 ppb leaving the water treatment plants; 0 ppb for tap water in most homes, and 2.3 ppb in homes with lead service pipes.  These results are well within the Canadian and U.S. health-based targets for lead in drinking water.

The situation in Ottawa’s water supply is quite different.  The treated water produced by the City of Ottawa Water Purification Plants is lead-free.  However, trace amounts of lead can dissolve in the water as it travels through a lead service pipe or when it comes in contact with household plumbing components such as lead solder and brass fittings.  It should be noted that there are no lead watermains in the City’s water distribution system; however, there are lead service pipes that connect the watermains to the customers’ property line.  For homes constructed before 1955, lead service pipes were commonly used until the plumbing standard switched to copper service lines in 1958.

There are approximately 30,000 older homes in Ottawa that originally had lead service pipes connecting the watermain to the home.  Over the years, the City has replaced the public portion of the lead service pipe with copper, usually when the watermain is replaced or upgraded.  Today, it is estimated that there are approximately 15,100 homes remaining that still have lead for the public portion of the water service pipe.  Since the private portion of the service pipe is the responsibility of the homeowner, it is not known how many of the 30,000 private services have been replaced.

For many decades, the City of Ottawa has practised corrosion control at the water purification plants.  Before treated water enters the distribution system, the pH is adjusted to a level of 9.2 (pH units) in order to reduce corrosion within the water distribution system and to minimize the amount of lead or other trace metals that can dissolve into household tap water.  This corrosion control strategy was further enhanced in 2002 following 2 years of extensive research and testing.  It has proven to be very effective at minimizing trace metals in tap water throughout Ottawa.  In fact, Ottawa tap water has some of the lowest measured levels of lead in Ontario.

Starting in 2007, a new Ontario regulation was introduced that requires water utilities to randomly test tap water lead concentrations in 50 – 100 homes every six months.  Homes with lead service lines are specifically chosen in order to represent the “worst case” levels of lead that might be observed.  The testing is conducted during winter and summer periods to represent any seasonal changes in water quality.

Since 2007, Ottawa’s tap water lead testing has consistently passed the criteria for safe drinking water.  In order to meet compliance standards, 90% of the tap water samples must have a lead concentration below 10.0 ppb following a 30-minute period of stagnation in the plumbing system.  Combining results for all 14 rounds of testing for 2007 – 2015, the average lead concentration in homes with lead service pipes is 2.3 ppb, and 90% of the homes had lead levels less than 4.9 ppb.  During the 2015 round of testing, there were 4 samples that had lead levels higher than 10.0 ppb, out of 222 samples taken.  The maximum concentration detected was 14.4 ppb.  Typically, these are homes with longer than normal lead service lines supplying their home.  In each of these cases, homeowners were notified immediately and provided with practical advice for reducing lead in their tap water, and to offer further water quality testing.

Several recent media reports have mentioned an increased risk of lead exposure following partial replacement of the lead service pipe, especially following construction to replace water mains.  This effect has been observed in several North American water utilities in recent years, and is thought to be caused by electrochemical reactions between dissimilar metal pipe materials such as copper and lead.  In Ottawa, several research studies have been conducted to specifically look at this issue, including research by Marc Edwards (Virginia Tech) and Michele Prevost (Ecole Polytechnique).  For Ottawa, the observed increase in lead levels was minimal.  It was found that tap water lead concentrations quickly returned to normal or lower values following replacement with copper/lead.  The researchers concluded that the pipe mineral scale in Ottawa’s system was particularly stable, due to our specific water chemistry and years of corrosion control being practised.

If a customer wishes to remove their lead service pipe, they can apply to Ottawa’s Lead Pipe Replacement Program.  This is a shared cost arrangement in which the homeowner pays for replacement of their privately owned portion (from property line to house) and the City replaces the publicly owned portion (from watermain to property line) so that the entire water service pipe is lead-free.  The City also proactively offers this program to residents who are impacted by a City Watermain Replacement Project that could have lead service pipes.  For more information on water quality and the City’s Lead Pipe Replacement Program, please visit www.ottawa.ca.