harvesting rainwater

The Red Hose, 1981

Harvesting of rainwater is the collection of water for domestic or commercial use that would otherwise go down the drain. Various techniques have been practised for thousands of years to collect and store water, especially in areas of low rainfall. Today, rainwater harvesting systems can be installed in both new and existing buildings and can range from a quick, cheap water butt to a more complex system.

The simplest collection method is a rainwater butt connected via a diverter to a downpipe from the roof - water collected can be used on the garden, using a watering can. More info here too.
In a rainwater system, water is collected from the roof and taken via pipes to a storage tank. A filter removes leaves and other debris and a settlement tank allows small particles to sink to the bottom; floating debris is skimmed off the surface via an overflow pipe, and clean water extracted from just below the surface. Water can be pumped directly from the tank to appliances or to a loft header tank. A float switch in the tank will automatically top up with mains water if the level is too low

The benefits of harvesting rainwater:
• rainwater collection removes the need for the energy and chemicals used to produce pure drinking water - unnecessary if all we’re going to do is clean the car with it or flush it down the toilet
• it also reduces the need for the pumping of mains water, and the energy use, pollution and CO2 emissions that go with it
• it reduces demand on rivers and groundwater:
• other benefits: rainwater is soft, and leaves no limescale; washing clothes in soft water requires less detergent and so reduces water pollution from these compounds; plants love rainwater; it doesn’t contain chlorine, which is thought to be carcinogenic; large-scale collection of rainwater can reduce run-off and therefore the risk of flooding

How do you get started?

First, cut your water use: average UK per head domestic water use is around 55m³/year (160 litres / day). This can easily be cut to less than 30m³/year by installing low-flush toilets (or better still, compost loos), getting rid of the dishwasher, fixing dripping taps, washing the car less often, and having showers instead of baths (especially if you share with a friend). Then find the rainfall figures for your area and your roof area, and see how much water (in m³) you can expect to collect per year. For an average property with average rainfall, you should be able to get around 100m³. Water is metered at between £1-2 per m³. If you’re not metered, your water supplier is obliged to install one for free (currently around 25% of UK households are metered).
The costs of a rainwater harvesting system are in the region of £ 1000 to £ 1500 and may be prohibiting. Maybe rainwater harvesting is something you want to do regardless of length of payback time.

There are no UK regulations concerning rainwater use for toilets, washing machines and gardens, though the back-up from the mains must be in accord with standard regulations.

At downshifting path, we are not in a position to install a rainwatersaving system as such, but all watering in the garden is done either by natural means ( monsoon rains currently), or water butts, or using the submerged claypot irrigation system. We also mulch and plant plants closer together in raised beds to minimise evaporation of water on sunny days.