Rain Water Recovery

What is rainwater harvesting?

Rainwater harvesting is the capture and storage of rainwater from the roofs of buildings for recycling and reuse through the building. People throughout history have harvested rainwater and although industrialised areas have tended to move away from it, rain water collection is becoming more popular and necessary due to ecological concerns. The reclaimed rainwater is filtered and reused, typically to supply WCs, washing machines, water for gardening (even during a hose pipe ban) and car washing. In commercial applications rain water can also be used for cooling systems, industrial cleaning and fire fighting.

The advantages of harvesting rainwater systems

There are many advantages of rainwater harvesting. Where expensively treated and transported drinking water would otherwise be used, rainwater becomes the substitution. This reduces environmental impact and demand on precious water reserves. Efficient and economical recycling of rainwater will reduce water and sewerage bills and increase appliance lifespan as rain water is better than mains water for washing machines in hard water areas, reducing scale and detergent use. Reclaimed rainwater is also better for irrigation as it is ideal for plant growth and rain water recycling can reduce stormwater run-off helping with flood prevention.

Rainwater harvesting - things to consider

The main factors that will be considered by the building services engineer are the roof type and orientation, the location and the demand.

The area of the roof, the roof material and the pitch, along with the average/likely rainfall in the location, will determine how much water can be collected. The rainwater collection tank should be designed for a reasonable turnover period. The system designer will need to know as accurately as possible the occupancy profile of the building and the number of WCs, urinals and any other appliances which will be served by rainwater.

If the building is to be BREEAM assessed a rainwater recycling system can help to add credits, but it must fit the relevant BREEAM criteria.

Any other site specific peculiarities will need to be examined, for example if you there is shallow drainage or siphonic drainage these will require special measures.

Specific rainwater harvesting products listed on the Water Technology Product List may qualify for Enhanced Capital Allowances allowing 100% of the investment cost to qualify for relief against business profit made during the investment period.

Rainwater harvesting systems

Rainwater is collected and generally undergoes filtration or other treatment in a below ground tank. The treated recovered rainwater is pumped, in some systems up to a header tank located on the roof or in a roof void, and then distributed throughout the building for non potable use.

Users often opt for extensive monitoring of rainwater harvesting systems as the data can be used for education in schools and generally to advertise the environmental credentials of the building. Data concerning the quantity of reclaimed water can be displayed on a screen in the building entrance or other public area.

Have a look at our project Piccadilly Gate which incorporated a rain water recovery system.