The next time you take a dip in a pool or hot tub, you might want to think about what you're sharing with your fellow swimmers -- it could be more than chlorinated water.

It's uncomfortable to consider, but substances that we would never consciously eat, drink or put on our skin appear regularly in our pools, and our own bodies are the primary culprits.

Many people get sick each year from germs picked up in swimming pools or hot tubs. Chlorine helps, but being conscientious about our pool hygiene can also reduce the risks of waterborne illness when we swim.

Most people know to avoid drinking pool water, and instinctively avoid swimming where it doesn't look or smell clean. But it's also important to think about what we personally bring to the communal dip.

If you're just hopping in to rinse off, in other words, please consider rinsing off in your own shower.

Germs that can make us sick travel effectively into the water from trace amounts of waste on our bodies. The most common harmful bacteria that we catch in our pools cause diarrhea.

If you don't wash your hands after using the bathroom, you will probably spread potentially harmful bacteria. If you then jump into a pool, you're even more likely to share those germs.

That's because chlorine and other pool disinfectants, while effective when used properly, can take hours or even days to kill all the germs. It depends upon the kind of bacteria, the chemicals used, and other conditions in the pool.

So the more contaminants introduced, the more likely that someone in the pool will be exposed to enough to get sick. That's why being mindful of our personal hygiene matters when we swim.

Don't swim when you're already sick.

Young children who are not yet toilet trained can contaminate water quickly. Taking any child who still needs diapers into the pool is risky, and parents should never allow kids wearing diapers into the pool. I'm also skeptical of products marketed as "swim diapers."

If you do take young children to the pool, it's extremely important to never change a diaper beside the pool. Always go to the restroom, dispose of the diaper properly, and make sure you wash your hands before returning to the water.

Young kids who swim should also make pit stops every 30 to 60 minutes.

Swimming can be a lot of fun, but remember that chlorine only helps so much. To stay healthy and safe this summer, please use common sense and courteous pool hygiene.

Susan Farley is the communicable disease controller for the Public Health Division of Contra Costa Health Services. Send questions to series coordinator Dr. David Pepper at theairdoctor@gmail.com. For more health information, go to www.cchealth.org.