Rain-drops keep failing on my head - why rainwater harvesting is important

“Into each life some rain must fall” noted the poet Longfellow, although with this years higher than average rainfall across the UK many may rightly feel that his observation was somewhat understated. Indeed, with the exception of the south-west, the whole country has experienced above average rainfall when compared with the average for the years 1961 to 1990. It is therefore hardly surprising that as a nation we are complacent about our water and possibly explains why our water prices are cheaper than many other countries.

Despite the fact that we appear to have plenty of rain, the UK is classified as a country with insufficient water. A growing population (8% since 1971) has meant that our water resources are actually under pressure and provide the rather surprising fact that Madrid and Istanbul have more water available per person than London.

Price Rise

The days of cheap water may also be about to change with water prices set to surge above the rate of inflation between 2010 and 2015 if regulator Ofwat allows. Thames Water, the UK’s largest water company, says it expects bills to rise by 3% above inflation a year and United Utilities plans to raise its process by 2.7% also above the rate of inflation. A decision from Ofwat is expected by November 2009.

Where does all the rainwater go?

Only some of the rainwater that runs off our roofs finds its way into the water table and thence into the source that the water companies draw from. The vast majority of rainwater flows off down rivers and into the sea. It was been estimated that as little as 1% is drawn out for mains water with the remaining 99% being ‘lost’ into the sea without ever being processed through the mains water system. If the rainfall levels reduce again in the coming years the 1% becomes an even smaller volume of water and the pressures upon the supply are increased.

Reduce pressures on water resources

Rainwater harvesting does not reduce the amount of water that is available to the water company, but it does of course, reduce the load on the mains supply and hence the total amount of water that the water company has to source, transport, clean, purify, stock and ultimately deliver. Consequently it reduces the amount of energy, electricity and fossil fuels that water companies consume to operate.

In addition to the pressures on water resources, there are concerns over rainwater drainage. The terrible consequences of flooding mean that our existing approach to rainwater drainage systems will have to change. The Environment Agency is promoting the use of sustainable drainage systems, including rainwater harvesting, to retain and control surface water.

Rainwater harvesting

The concept of rainwater harvesting is thousands of years old, although over the last century its use diminished with the availability of a clean, inexpensive and reliable water source through the mains supply. The practice has been kept alive by gardeners and many households with gardens have rainwater butts.

Modern domestic and commercial rainwater systems simply collect the rain which falls onto the roofs, stores it is a tank until it is required for use, when it is then pumped to the point of use which is typically services such as toilets.

Increase in interest

Although still not widely used in the UK, rainwater harvesting systems are increasingly being incorporated in multiple occupancy commercial and public-sector developments such as office buildings, schools, and hospital extensions where their use makes excellent financial sense with typical payback periods of three years.

Distribution centres with their requirement for fleet vehicle washing also are an excellent example of the cost-effective application of rainwater harvesting. In short, any building with a large roof and a high-demand for non-potable water can effectively use rainwater harvesting to help solve environmental storm-water management issues - and make very substantial savings on the use of mains water.

Why should the air-conditioning and refrigeration industry be interested?

The evaporative effect of water plays a significant part in the energy efficiency of many cooling systems by using water in the cooling towers or evaporative condensers. Such systems are frequently used on large buildings that would be very suitable for rainwater harvesting systems. By encouraging the use of such systems we can reduce the carbon footprint of the plant still further and be a proactive partner with the client in their drive for reducing their environmental impact as well as their operating costs.

Ella Fitzgerald added to Longfellow’s words when she sang “Into each life some rain must fall, but too much is falling in mine”. With a rainwater harvesting system, perhaps that is not such a bad thing.