Specifier Review
Why rainwater harvesting is becoming a necessity

Why rainwater harvesting is becoming a necessity

Author: Marcus Bicknell Of Rainwater Harvesting Ltd 

With The Environment Agency And Defra Declaring Much Of Southern And Eastern England Officially In A State Of Drought, There Has Never Been A More Appropriate Time To Consider The Efficient Harvesting Of Rainwater. Marcus Bicknell Of Rainwater Harvesting Ltd Explains How Systems Are Easily Installed And Their Water And Money Saving Benefits.

With hosepipe bans in place from April by seven water companies in south east and eastern England, the time has come to invest in large capacity rainwater storage tanks. To promote saving on mains water use, the official stance currently places great emphasis on changing our water use behaviour by, for example, taking shorter showers and not leaving the water running while we wash our teeth.  We are also encouraged to install water efficient appliances such as slow running taps and low-flush WCs.  This is all very commendable but it is a pity that not more incentives are taken to encourage the take-up of rainwater harvesting as well.

Climate change, population growth plus our hunger for water-greedy appliances in the home have all put a great strain on our aged mains water supply network.  Even with modernisation, our mains water supply will not be able to fulfil our needs in the future.  Rainwater harvesting could be a key way to supplement mains water supply.  30% of mains water goes down the toilet, and by using rainwater not only for WCs but also for the washing machine and outdoors, we can save 50% on mains water. Rainwater can be used for any use that does not require drinking quality water.

Installing A Rainwater Harvesting System

Installing a rainwater harvesting system is not complicated. To harvest rainwater productively it is essential to invest in a large capacity storage tank. Most people now realise how quickly the typical 200 litre butt they have in their garden will run out in dry weather (20 watering cans’ worth).  Conversely, this same butt will overflow in a few minutes in a torrential downpour such as we tend to have in the summer nowadays. 10,000 litres of rain can fall on an average family home roof in a short storm.  Obviously the bigger the tank, the less likely is the rainwater to run out in a dry spell. For homeowner use, tanks will typically range from 2000 litres to 7000 litres.


For garden and other outdoor use, above ground tanks are a cheaper and easier option than below ground tanks, mainly because installation is cheaper as there is no hole to be dug. Underground tanks have two great advantages: the rainwater stays cool and fresh and the tank is out of the way.


Current Government Initiatives

 Building regs now force the private sector to take water consumption into consideration.   Building Reg Part G, 17K which came into force in April 2010  “requires that for any new dwelling the potential wholesome water consumption by persons occupying it must not exceed 125 litres per person per day”.  In the public sector, Level 3 of The Code of Sustainable Homes (maximum consumption of 105 litres a day) has been adopted for all social housing. 

Using Rainwater During Water Shortages

The Flood and Water Management Bill that came into force in April 2010 gave water companies the right to impose stricter rules during water shortages.  Before this Bill, hosepipe bans covered irrigation and washing private cars, but now – as large areas of England are now discovering – extends to include amongst others,  topping up pools, hot tubs, ornamental ponds and fountains whether with hosepipes or permanent plumbing.

Direct Or Indirect Supply Systems

Rainwater is taken from the main storage tank to where it is needed from a choice of two distribution methods. With “direct feed”, a pressure sensitive pump in the storage tank maintains pressure on the rainwater pipes typically to toilets, washing machines and for outdoor use. The pump will be activated whenever water is drawn.  With an indirect gravity feed system, the pump in the main storage tank supplies a header tank in the roof space, and the rainwater then gravity feeds to its destination.


Energy-Conscious Indirect Supply System

Where progress has really been made in reducing power use by the pump, is in the development of a special header tank equipped with electric float sensors so that the pump is activated to refill the tank only when it is completely empty rather than every time water is drawn. In this way, much less electricity is used.  In fact, power costs with this Rain Director® management system are estimated at only 1p per person a day.


Encouragement To Use Rainwater Harvesting

There are many variables to take into account to make accurate assessments of payback periods.  Water companies’ charges vary considerably, and so will the amount of rainwater used.  The figure used is a 50% reduction in mains water consumption.  Payback periods can be 6 years or more, but with water bills already set to rise by 8.8% next year, this time will lessen.

Encouraging consumers to use water-efficient appliances in conjunction with rainwater harvesting will make using less mains water a more attractive proposition and achieve the ultimate aim of reducing mains water use.