Rain water harvesting in a leafy London suburb

If its London, it must be raining ! This is the common thought that runs through most people's minds, so then where does the question of rain water harvesting arise?  Rainwater harvesting for me a journalist out of India is meant for countries with fresh water scarcity issues. Obviously that was an ignorant supposition as wasting of valuable rain water can happen anywhere in the world.  

Chatting with a London resident who lives in the leafy  London suburb of Woking, one finds that a system of 'harvesting' the rain has existed for decades here in London and he took me around his 100 year old home in Woking to explain the system.

"In Woking there is a system called a  soakaway where building regulations require you to adequately dispose of stormwater from the building. To try and ensure water is dispersed into the ground evenly and quickly you must consider the use of a soakaway in all homes, according to the council," explains David.

" You must use a soakaway, if design criteria can be met. Discharging stormwater into a drain will only be allowed if soakaways or other infiltration into the soil, methods are not suitable," said David.

So we were curious to know how  do soakaways work? Soakaways store the immediate stormwater run-off to allow infiltration into the adjacent soil. Then, they  must discharge their stored water sufficiently quickly, to provide the necessary capacity to receive run-off from a subsequent storm. The time taken for discharge depends upon the soakaway shape and size and the surrounding soil's capacity to absorb. Soakaways can be constructed in many different forms and from a range of materials .

Interestingly one cannot just build a soakaway without first checking if a soakaway is the most suitable means of disposing of stormwater. That is done by checking if the soil around the building can absorb water; the site is not on filled ground; the site does not slope towards the building and; the water table is not too high already. Other rules are that  soakaways can be sited at least 5m from any buildings and if one is close to boundaries the neighbour should be consulted.

The council gives guidelines which are interesting to read up on, regarding the building of the Soakaway In most cases where the soil drains well, and the roof area is less than 100m2, you will be able to construct an open chamber type soakaway, as follows:

Calculate the roof area to be drained into each soakaway. Then calculate the volume of the soakaway:

Roof area in m2 divided by 40 = Volume of soakaway in m3 (AxBxC)
The volume can then be measured below the incoming pipe and above top of foundation.

The council is particular that the  residents ask for an inspection of the drainage and the soakaway while it is being constructed.

David's soakaway was in the middle of his lawn! Well, if this can be done in London, why ever not elsewhere right?

Marianne de Nazareth