Grey Water Systems

Grey water is basically lightly contaminated waste water, typically from washing machines and shower/bathwater. Historically disposed of along with more contaminated waste water, grey water can be easily utilised for little cost and good benefit.

We use both bathwater and laundry water. In the case of the latter, I have connected the washing machine outlet to a nearby garden bed, the pipe terminating in a swirl sprinkler. This area was previously paved, but we converted it into a lush green space to moderate heat gain from the patio area into the house. This area benefits from all the laundry water, about 250L a week. 

One important factor in these systems is minimising strain on the washing machine, as the drain pump is not intended to be high-pressure pumps and can fail prematurely if overloaded. In our situation I have used 19mm poly tube, the same size as the washing machine outlet. Other factors to watch are that the water is not pumped uphill, that the pipe length is minimised, in our case to about six metres, and that the outlet will not clog up and restrict the water flow.

Also important to note is the kind of washing detergent you use. Make sure it is a low-phosphate variety otherwise it will overdose your plants and can kill them. Also important is that the detergent is easily biodegradable so that your garden doesn't get overloaded with chemicals.

For the bath water I've set up a simple pump system to transfer the water to our front garden. This west-facing area takes the brunt of heat during summer afternoons, the greenery acting as a welcome heat buffer for the house. Because this front garden is lower than the bathroom, the water actually siphons out of the bath so I only have to run the pump for a few seconds until water has charged the pipe.

One aspect to note is that grey water will contain bacteria so it should not be stored for more than a day. Care should be taken if it is used on vegetables.