Whenever we get close to a hosepipe ban, every "B-rate" celebrity gardener and water company spokesperson are on the TV telling us that used bathwater and washing up water is the ideal stuff to keep are lawns green and to stop our plants from wilting.
In the hose pipe ban of the early 80' s I diverted all our household waste water to garden irrigation. Any human waste has nitrogen content which all plants need. Coming from farming stock we regularly diverted the waste suckers to drop their contents on our fields for crop food. Excellent results every time. !