The Environment Agency predicts that demand for water in southern England may outstrip supply in the next 20 years. Yet public awareness of this problem remains low: 72% of people in a recent survey believed that the UK has enough water to meet the country’s needs.

The roof area of an average terraced house in the UK (30m²) receives between 19,000 and 55,000 litres of rain each year. Our modelling suggests that a significant proportion of household water consumption could be met by collecting this water.

Averaged across the UK, we found that a 210-litre rain tank – equivalent to a small bath – could supply 15% of a household’s total annual water consumption. 

But this statistic is subject to clear geographic and seasonal variation. In the wetter northwest of Scotland, we found that 26% of a household’s annual water consumption could be met by collecting rainwater. In contrast, only 9% could be supplied in the southeast of England, dropping to 4% in the driest months. Although this seems a low value, it still equates to 14 litres of water per household each day.

The calculation accounts for the loss of rainwater through processes such as evaporation. Current regulations also restrict the use of rain tank water to non-potable demands, such as flushing toilets.