Quote Originally Posted by mikewhi
Don't drink the water. Make plans on what water you'll drink when there. Be careful about ordering bottled water in restaurants as some places simply re-fill empty bottles from the tap. Don't brush your teeth with faucet water. When you shower, don't let any water get into your mouth. When eating out, don't order something that has been rinsed in water, like a lettuce salad or fruit salad.

I know that in some places down there, the sewer pipes (9-inch ceramic) are physically in the same holes as the water pipes. Each have numerous holes in them. When it rains, the sewer lines overflow and empty into the water lines thus contaminating the water. I don't know for sure if this is a problem in Oaxaco, but why risk it?
Mike is of course absolutely right about not drinking water from the tap, but not *exactly* for the right reason. There are no water lines in Oaxaca. Water is brought in trucks, labeled agua para humanos, and is stored in water cisterns. When the cisterns run out, that is the end of water for that residence, hotel, or what not until the water trucks arrive and pump more water into the cisterns. Obviously it is possible for the cisterns to become contaminated with sewer overflow.