Grey water is domestic waste water such as water used in sinks, showers, water taps and laundries but does include water from toilet systems. Grey water can be treated in a grey-water system that can make it potable enough for drinking purposes.

If not treated to drinking standards grey water can be used for other purposes at an event including watering local gardens, weighting marquees and to flush water-based toilet systems and at the same time save a significant amount of water.