Grey Water Recycling and Rainwater Harvesting

Grey water recycling within domestic homes is the process of taking used water from showers, baths and hand wash basins, filtering it and storing the filtered water for re-use. Rainwater harvesting systems substantially reduce consumption of potable water by using the roof as a collector of rainwater.

Technical information

Grey water recycling within domestic homes is the process of taking used water from showers, baths and wash hand basins, filtering it and storing the filtered water for re-use in flushing toilets, watering gardens and running washing machines. Grey water recycling systems can be connected in with rainwater harvesting systems to further reduce the use of potable water in situations where it is not needed around the home.

There are many different systems for grey water recycling varying from ones that are located underground like rainwater harvesting and collect water from the whole house, to ones that can be located in a single bathroom and collect water from just that bathroom to feed the toilet.

Rainwater harvesting fits in with the Codes for Sustainable Homes in achieving reductions in use of potable water which cannot realistically be achieved through water efficiency measures alone. It is estimated that up to 50% of domestic water requirements do not need to be of a potable quality. Harvested water can be used for flushing toilets, watering gardens and even used in washing machines.

Where possible install a gravity system which requires a header tank to be installed in the loft area which feeds from both the harvested water and the mains supply - the mains supply will only be used in the event of the rainwater running out. The advantage of this system is that it still works if there is a power cut or pump failure.

If it is not possible to install a gravity system, such as in a property with a habitable roof, then a direct system should be installed. This system requires a mains supply feed back to the harvesting tank that is controlled by a solenoid valve in order to keep the system running when there is no rainwater left in the tank.

Hints & Tips

If you are installing a new bathroom into an existing dwelling it could be a great opportunity to install a standalone system feeding from the new bathroom wastes to the new toilet.

Grey water recycling can reduce water drainage by up to 30% earning valuable points on the Code for Sustainable Homes.

The systems are easy to install and are often maintenance free so they are a ‘fit and forget’ system.

Rainwater Harvesting has an underground storage tank that should be installed on a concrete plinth and then encased in concrete to ensure the water table doesn’t lift the tank out of the ground when there is no water inside.

If installing a direct system and there are multiple toilets within the house, it may be a good idea to plumb one of the toilets with mains water so that in the event of a power cut or pump failure there is still a working toilet.

Ensure the pipework feeds from the rainwater harvesting tank to the inside of the house is installed with black and green striped pipework, so it is not mistaken for a blue mains water pipe.

Water usage is 125 litres per person per day.

The inclusion of rainwater harvesting can aid planning applications as local authorities increasingly expect applications to demonstrate Sustainable Drainage.