The most obvious benefit is the decreased usage of mains water. If you are on a water meter, every litre of water you use has a cost, so reducing that usage, means reducing cost and paying less on your water bill.
The Energy Savings Trust states that the average person uses 150 litres of water per day. As the table to the right shows, 30% (∴ 45 litres) of our average water use is for flushing toilets, so your water bill could be reduced by 30% just by using rain water for this simple purpose.
If you were to replace toilet flushing, clothes washing, and outdoor use this could mean replacing 50% or 75 litres of your water usage with rainwater that drops out of the sky for free.
| Usage | % |
|---|---|
| Toilet Flushing | 30 |
| Baths | 21 |
| Clothes Washing | 13 |
| Showers | 12 |
| Washing up | 8 |
| Outdoor | 7 |
| Other | 5 |
| Drinking | 4 |
No official studies have been done on the impact to house prices by installing a rain water harvesting system but we believe it will have a positive effect. It can become an interesting feature of the property that makes it stand out and we think buyers would be interested in paying less for water.
Not many people think of it, but every time you turn on a tap, you are using energy as well as just water. It takes energy to clean and process water and then pump it around the mains network. Like most of the energy on the national grid, this energy comes from carbon emitting fossil fuels.
WaterUK, the industry body for the water companies, tracks sustainability within the industry and the 2009/10 report (pdf) states that the sector average greenhouse gas emissions from supplying water is 0.34 tonnes per Ml of water (this is 340,000 grams per 1,000,000 litres = 0.34g per litre). This multiplied by the average daily use of 150 litres = 51 grams of greenhouse gas per person per day.
Therefore, the more mains water you save, the more carbon you are saving. If you reduced your mains water use by 50%, that would save 20.5g of greenhouse per person per day. Rainwater harvesting does require some energy to pump the water from the reservoir to the header tank, but this is far less than moving the water over a large area and at high pressure.
The Energy Saving Trust has a fun and informative tool that lets you calculate your likely water use, energy use and CO2 emissions.
When rain falls in a rural setting, much of it will soak into the ground. In an urban environment, much of the landscape is impermeable so the water will not soak away and will run across the surface into rivers and drains. Flooding often occurs when the rain water is not able to drain away fast enough.
It is much harder to quantify the impact and we won't claim rainwater harvesting would stop all flooding, but imagine how much rain water would be held safely if everyone had a 100 litre storage reservoir.
There are people in the world dying due to lack of access to clean water. Yet in the UK we take time and energy to filter water to strict levels of cleanliness and then use litres of this precious resource to flush away waste.
Often just knowing this is enough to motivate people to reduce their usage of clean, potable water and try to utilise a free resource that falls around them from the sky.