If you have a backyard pool that uses chlorine to keep it clean, you can reuse the water when it's time to drain the pool to get it ready for the fall and winter months. The first step: Stop using chemicals altogether and wait half a week. This will reduce the pH level of the pool water to a safe and acceptable level. You can rent an electric pump from your pool supply store and attach a hose to it; as it siphons the water, you can use it to water the lawn, plants and other landscaping. Remember, discharging chlorinated water into the drainage of your own property is illegal in most communities, so these simple actions can make a big difference.