I know longtime readers have heard this before, but it is apparent from several letters that it bears repeating.

Please, when you write to me concerning your pets, use their names. When you don't, I am forced to make one up and I am sure that your pet, upon reading the article, feels somewhat insulted.

Rover is a 10-year-old Lhaso Apso who, according to Don, has been active all his life. Don said Rover had a bout with bladder stones about three years ago and has been on a special diet to help prevent their recurrence. Don wants to know about Rover's apparent water preferences.

Although Rover is provided fresh water daily, he appears to take only a few laps from his bowl. Instead, he seems to enjoy drinking from standing water in the gutter and any other stagnant puddles he might encounter while out walking.

Don is probably concerned about potential health problems associated with this behavior. I suspect many of us are. I've seen my dog drink from ponds with all kinds of biologic material growing in them. He had even been known to partake of the ocean on occasion. Was I concerned? Maybe the first few hundred times, but since my concern was never really validated, it kind of disappeared. However, this scenario is not always the way it works.

Stagnant water sources and, for that matter, some running water sources can contain potentially harmful entities both living and nonliving. Gutter water specifically can contain chemical contaminants, usually from automobiles, that can be toxic to pets. Antifreeze probably has the greatest potential for harm. The most common chemical used in antifreeze is ethylene glycol, and ingestion of relatively small amounts can be deadly.

Standing pond water contains bacteria and algae, but most are harmless, although some types of algae, specifically the blue-green algae, can be highly toxic.

I did mention that running water intake can cause problems. Obviously, any chemical contamination, whether the water is standing or running, can be toxic depending on the chemicals and concentrations. There are also potential biological contaminants that can occur in running water. Giardia comes to mind. This is a protozoal organism that causes gastrointestinal disease. There are other protozoal organisms that can cause gastrointestinal disease, and perhaps some of you have suffered the effects after drinking water from less-than-pristine sources. Remember that trip to Mexico? They told you not to drink the water. And even if that beautiful mountain stream is crystal clear, some animal probably has defecated in it somewhere upstream and may have introduced an offending organism.

Now that I have properly scared everyone, I must tell you that in my clinical experience as a veterinarian, I have seen few problems that I could attribute to drinking water from other than their bowls. I can tell you from firsthand observation that drinking from the ocean can mimic the effects of a laxative.

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(Jeff Kahler is a veterinarian in Modesto, Calif. Questions can be submitted to Your Pet in care of LifeStyles, The Modesto Bee, P.O. Box 5256, Modesto CA 95352.)