An increasing number of households in the UK are being built or retrofitted with rainwater harvesting systems for use with greywater appliances – including washing machines, toilets and garden sprinklers. While this makes obvious economic sense during the rainy days of autumn and winter, do the sums still hold up in spring and summer?

Keeping The Garden Watered

This is an important question because some of the most popular rainwater harvesting systems are small, relatively cheap units that collect water exclusively for use in the garden. These garden rainwater harvesting systems are fast and nonintrusive to install, and ensure that household gardens are irrigated at the times of year they need it most; the dry days of high summer.

Unlike arid parts of the world where rainwater harvesting systems are popular – such as Arizona and Australia – in the UK we have plenty of rain all year-round. Average annual precipitation between 1981 and 2010 was 33.7 inches (885 mm) across the country, with rain or snow falling on 133 days of the year. The wettest recorded place in the British Isles was Princetown in Dartmoor, Devon, which experienced an average 78.7 inches of rainfall across 183 days each year, while the driest, Cambridge, still had a healthy average of 22.4 inches.

Britain is not called a green and pleasant land for nothing!

Is Rainwater Harvesting Necessary?

With all this rainfall, do British households actually benefit from installing a rainwater harvesting system for their garden? We believe so, yes. Look at last summer (2018) for instance. June and July 2018 were hotter than average, with some parts of the country experiencing 50 consecutive days without rainfall. Weather stations across the country recorded 48% less precipitation than the 1981 to 2010 summer average. Lawns and parks across the country turned a Mediterranean yellow for several months, rather than their customary lush green.

During heat wave summers such as this, rain harvested during the autumn, winter and spring can be deployed in the garden to keep plants healthy, without depleting precious mains water. Even during an average or wet summer, temperatures can be high and rainfall sporadic, and not always focused on where it is most needed – i.e. your garden! The advantages of rainwater harvesting in the spring and summer include a greater flexibility in how you use your garden, with more water available to achieve the garden you want without having to worry about hosepipe bans and sustainability. Households that use garden rainwater harvesting also use less water throughout the year, resulting in lower water bills.

There are three main types of rainwater harvesting system: direct pumped, indirect pumped, and indirect gravity. In certain situations it may be possible to have a purely gravity system; though such occasions are rare.