Reusable water bottles are good for the planet, since you can use them over and over again. But reusable bottles need to be taken care of to help you stay healthy. If you don't wash your reusable bottles, the interior cavity can become a breeding ground for unhealthy bacteria. Make sure to fully dry the bottles after you wash them, too, otherwise, they can make you sick the next time you fill them up. Another idea: Place clean bottles back into the fridge. The cold air inhibits the growth of bacteria. And on a hot summer day, the bottle will keep your water chilled even longer.