Grey water derives its name from its appearance which is cloudy and refers to water that is in between ‘white water’ (uncontaminated water) and ‘black water’ (contaminated water). Leftover water from kitchen sinks, clothe washing machines, bathroom and lavatories are referred to as ‘grey water’ while leftover water from toilets is not considered as gray water. Gray water system then refers to re-use of leftover ‘grey water’, excluding that from the toilet, for irrigation purpose or other uses. Grey water in some states is considered to be unsafe for use because it has a lower quality than tap water but compared to that from sewerage, it is more nutritious and safer. Filtered gray water is used for irrigation purposes because it contains nutrients that help the plant to grow. In the floor plan illustrated below, the gray water system will be installed on the terrace, which is a raised part that is used for plantation purpose and application of irrigation.


The amount of gray water to be used will depend on the size of the plot and the landscape to be irrigated. The building to be built will generate water for the gray water system and plumbing fixtures will be connected to the sources which include ; kitchen sink, clothe washing machine, lavatories, and shower tubs. A settling basin will be installed at the first receiving end to equalize the flow of water and allow settling of particles. The gray water will then be allowed to flow into a storage tank which contains a filter to further clean up the water. Water entering the tank should not be allowed to stay more than 24 hrs because it might generate a foul smell. The filtered water will then be passed into the irrigation drip system where it will be spread to areas that need to be irrigated. The irrigation system should be designed in such a way that it allows gray water to drain back into the tank when the cycle is complete. It should contain a timer which will ensure that there is enough water for the process to start. The irrigation heads should be installed in the ground near the plant to be watered.