Floods can contaminate the water you drink, making a bad situation worse. Obviously, the simplest step is using bottled water if you can. If that's not available, follow this advice from the U.S. Department of Agriculture:
If you don't have bottled water, boil water. That kills most types of disease-causing organisms. If the water is cloudy, filter it through clean cloths or allow it to settle, and draw off the clear water before boiling. Boil the water for one minute, let it cool, and store it in clean containers with covers.
If you can't boil water, disinfect it with household bleach. Bleach will kill some, but not all, types of disease-causing organisms that may be in the water. If the water is cloudy, filter it through clean cloths or allow it to settle, and draw off the clear water for disinfection. Add 1/8 teaspoon (or 8 drops) of regular, unscented, liquid household bleach for each gallon of water, stir it well and let it stand for 30 minutes before you use it. Store disinfected water in clean containers with covers.
If you have a well that has been flooded, get it tested and disinfected as soon as possible after the flood waters recede. If you think that your well is contaminated, contact your local or state health department or agriculture extension agent for specific advice.