The city has closed five public wading pools for cleaning this week because of poor water quality, but health officials say the dirty water is not behind an increase in E. coli cases in Calgary.

Hot weather and more than the usual number of bathers are to blame for the dirty pools, said Chad Beegan, the environmental health co-ordinator for the Calgary Health Region.

He urged parents to use their own common sense in assessing whether a pool is too crowded or too dirty for their children.

"Analyze the water quality, look to see if the water is cloudy or not, take a look at the bathers and the behaviour they are partaking. Take a look to see if the diaper-age children are wearing protective diapers," he said.

"If it looks too crowded to you, it probably is."

Dr. Judy MacDonald, the deputy medical officer of health for the Calgary Health Region, said Friday that there isn't a link between a rise in E. coli cases and the water in city wading pools.

This month, 28 cases of sickness from E. coli have been reported in Calgary, compared to five last July.

"We still don't know what the source may be and the investigation is ongoing, trying to get more and more detail," MacDonald said. "We do have several clusters, meaning they are related to one another."

MacDonald says statistics on people who fall ill with E. coli vary from month to month, but there are always more cases in the summer months. People should cook food properly and wash their hands to avoid getting sick, she said.

E. coli, or Escherichia coli, is a common and ordinarily harmless bacterium, but certain strains can cause abdominal cramps, fever, bloody diarrhea, kidney failure, blindness, paralysis, and even death. It is most often spread through contaminated food.