The concept of rainwater harvesting has been well-documented from the pre-Roman times [1], however this practice has largely died out in industrialised countries with the introduction of mains-supplied water. As there is an ever growing demand for water (and a consequential rise in costs), it seems ludicrous that in the UK we use drinking water to flush toilets, wash vehicles, do the laundry and water the garden! It has been shown that 55% of domestic treated water could be substituted for rainwater and 85% of water used in industry does not need to be of drinking standard [2]. Consequently to conserve water stocks, the UK demand for rainwater harvesting systems is on the increase, just like it has been already in other industrialised countries.
How Rainwater Harvesting Works
Rainwater harvesting systems operate using a typical roof drainage layout where rainwater runs down the roof and into the guttering. It then flows down the pipes in the normal way before passing through a filter to remove the leaves and debris. The rainwater is then stored in an underground tank containing a pump and filter which respond when the water level begins to decrease. This water can be used, with or without the addition of a header tank, in non-potable ways such as flushing toilets, washing vehicles and washing clothes. Unfortunately, this system is not usually fitted on to existing properties as extensive internal plumbing and building work is required, however the cost is often negligible in newly built houses. There is the option of a more typical “retro-fit” rainwater harvesting system designed mainly for watering the garden. Gardens can consume up to 50% of peak water demand in the summer season, so harvesting rainwater may save thousands of tap water a year and cut your water bills and energy usage. An example of this is the Kingspan Raintrap, which collects, filters and stores the rainwater in a storage tank where it is then pumped under pressure from the tank to a hose or sprinkler which prevents constant trips back and forth to the water butt. This system can also benefit the plants as they thrive on the warm, soft, chlorine-free rainwater and it requires no internal plumbing work so can be easily installed.
The Costs
It can cost between £2000 and £3000 for a good quality domestic system depending on the size and industrial systems can be much more expensive [3]. Although this is quite steep, the payback period can be as low as 2-5 years for commercial systems and between 10-15 years for domestic systems, depending on water costs in your area [4]. Independently monitored domestic installations show that almost all the requirements for non-potable household systems were met – saving around 50% on main water consumption [5].
What You Can Save
The UK Rainwater Harvesting Association has estimated that a full rainwater harvesting tank for a two-storey house with a 100m2 roof can provide enough water for 200 flushes, 30 full washing machine cycles and 12 car washes. This could equal an annual saving of £256 for a property on a water meter. So therefore, rainwater harvesting not only reduces water consumption and helps to conserve water supplies, it can also save you money on your water and energy bills.
[2]http://www.waterwise.org.uk/reducing_water_wastage_in_the_uk/house_and_garden/guide_to_rwh.html7
[3] http://www.ukrha.org/rwh/faq/21
