In plumbing terms, there are three kinds of water. White water is the water that comes in through your faucet and is safe for drinking. Black water is the water that goes out through your toilet, and isn’t safe for anything. And grey water is the water that goes down your drains after being used to wash your dishes, your clothes, or yourself. While you shouldn’t drink it, it’s still good for many other purposes.
For example, some buildings route the greywater that goes down the bathroom sink into the toilet tank. Then, the toilet can be flushed with water that was already used for washing hands, instead of with clean, drinkable water.
Similarly, water that’s been cycled through the dishwasher or washing machine can be used to water plants. Some people have plumbed their houses to drain this water into a rain garden or similar system. The water then gets filtered by the plants, instead of being filtered by a municipal system on the taxpayer’s dime.
Greywater systems are a great way to use resources more efficiently, conserving water and saving money. Unfortunately, they are not legal in many cities, because health departments worry that the slightly-dirty water could transmit disease if drained into yards instead of into pipes.
These fears are largely unfounded. If a greywater system is set up properly, and care is taken to not put toxic soaps or other harmful substances into the system, then recycling greywater is safe for people and the environment.
As water shortages become more severe, greywater systems are likely to become legal in more places. Citizens can ask their elected officials to not delay legalizing this simple way of using resources more wisely.