Ontario's environment minister expressed anger Thursday that it took 19 days before he was told about bungled water testing, but insisted the province's tap water is safe.

Chris Stockwell told the Ontario legislature that the ministry was informed by a whistle-blower on May 23 that a lab in London was not adequately testing for E. coli in drinking water for 67 cities and towns, mostly in the southwestern part of the province.

He said officials performed an inspection of MDS Laboratory Service on June 5 and told him of the problem late Tuesday.

On Wednesday, Stockwell's department sent an urgent memo to 270 waterworks in 67 cities and towns, warning them that MDS Laboratory Services failed to meet rules for water testing.

"I don't want to say heads are going to roll, but I'm not happy,'' said Stockwell, who has ordered an investigation into the department's actions. "Common sense tells me it took too long.''

Both the Ontario Liberals and New Democrats accuse the province's Conservative government of failing to protect drinking water for a second time. In May 2000, seven people in Walkerton, Ontario died and 2,300 became ill from water tainted with E. coli.

"The only thing that is protecting Ontario families when it comes to what is going on inside private water-testing labs is anonymous tipsters,'' said opposition leader Dalton McGuinty.

"Who is supposed to be ultimately responsible for safe and clean drinking water?'' said McGuinty. "It's not some damn private labs. It's this government.''

Stockwell has ordered drinking water samples from the London lab be retested but said the chance E. coli actually got into drinking water again is "close to zero."

"There is no indication the water is not good. There is no indication they had faulty tests. They just didn't complete all parts of the tests," he said.

At this point, no one has been reported sick and no boil-water advisory has been issued. But critics are outraged, saying the health of hundreds of thousands of people has been put at risk.

"It means that Ontario's water is still at risk despite assurances of several ministers of the environment, including two premiers, we still have a situation where our water is not being adequately tested," said Jim Bradley, the Liberal Environment Critic for Ontario.

MDS said Wednesday there had been "some problems" with reporting during the recent strike by the Ontario Public Service Employees Union. A spokeswoman said the company was confident that all adverse results had been reported, and all reporting that was sent to the government was accurate.

Stockwell also denied that under-funding led to the lapse in testing. "I just don't believe it's a money issue," Stockwell said.

A list of some of the municipalities and other users of MDS laboratories, which may not have tested properly for E. coli in their drinking water:

Arran-Elderslie Aylmer Bayham Bluewater Brant County Brantford Brooke-Alvinston Central Elgin Central Huron Chatham-Kent Chatsworth City of London Dutton-Dunwich Elgin Primary Board of Management Enniskillen Erin Georgian Bluffs Goderich Gore Bay Grimsby Guelph Haldimand Hanover Huron East Huron-Kinloss Kincardine Lakeshore Lasalle Leamington-Kingsville-Essex-Lakeshore Lake Huron-Primary WSS Joint Board of Management Lucan-Biddulph Malahide Mapleton Meaford Middlesex-Centre Minto Morris-Turnberry Newbury North Middlesex North Perth Orillia Owen Sound Oxford Country Penetanguishene Perth South Petrolia Plympton-Wyoming Point Edward Sarnia South Bruce Pensinsula South Bruce South Huron Southwold St. Catharines St. Marys St. Thomas St. Clair Stratford Strathroy-Caradoc Thames Centre Warwick Welland West Elgin West Lincoln West Nipissing West Perth (Source: Ontario Ministry of Health)