Rain water harvesting is incredibly popular in the UK but it is generally done on a very small scale, using water butts next to gutter down-pipes. Typically 100-200 litre water butts are used because they don't take up much space and they are generally not attractive things to look at. Having said that, you can get water butts that in various styles, shapes and colours, to better blend into their environment. In countries where there is limited rainfall (e.g. Australia), rain water harvesting is a big deal and is taken very seriously. In some more remote places, it is the only source of water for a property. The simple fact is that climate change and population growth are going to place increasing demands on water supplies and increase the cost of water delivered by the mains network.
Rain water harvesting can provide more than 50% of the water required by a typical property and can be used for garden taps, washing machines, toilet cisterns and utility rooms. With large gardens, it is likely to be the only cost effective way to irrigate decorative flower beds and vegetable plots. The collection of rainwater can also reduce surface water around your home and help handle the excessive volumes of water from heavy storms.
Here in Suffolk, we have a very dry climate and hose pipe bans are becoming and annual occurrence. As well as saving you money, rain water harvesting can be the difference between keeping your garden alive through long, dry summers or not. Combined with greywater recycling, it can make a significant difference. The rain water collected is also much softer than the mains water and thus less detergents are required, when it is used in washing machines, etc.
Rain water harvesting also helps with 'rain water attenuation' (also called storm water attenuation), which means it reduces the amount of water going into the local drainage system in periods of heavy rain and thus reduces the chances of them being overloaded.
The pay-back period of rain water harvesting is typically around 7 years, which is much better than many environmental systems. The ideal time to install rain water harvesting is as the foundations of a house go into the ground.
You can collect rain water in simple open containers but to collect rainwater effectively, you need to collect it falling on large areas. For most people this means the roof of a building, using the gutters to bring the water to one or more collection points. It is also possible to collect water as it runs off fields, patios, driveways and other large ground-level spaces though.
Typically, the rain water is diverted towards a storage tank along its way to a main sewer or drainage system and then stored in a tank. Once the tank is full, the excess or overflow is fed back into the sewer. It is vital that you have a reliable way to feed excess water back into the sewerage system before you start diverting in into storage tanks!
On a small scale, it is possible to use diverters installed in existing down-pipes but, these to not always have filters and because of the narrow bore hoses used, these devices are easily clogged by moss and leaves.
Rain water really needs to be filtered before it is stored and the filter needs regular maintenance, so must be in an accessible area.
In the UK, most people use 100-200 litre water butts for storage of harvested rain water but, this is relatively small scale and will not meet the needs of most small gardens over a long hot and dry summer. In order to store sufficient rainwater over the wetter, winter months, you will need to use a much larger tank. Because of their size, these are often installed underground.
Larger tanks can be 'slimline' and located up against walls. Storage capacity can be increased by adding new tanks over time.
If space permits, then really large (>5000 litre) tanks can be used but these can be unsightly and are usually hidden behind screens or buildings.
Larger tanks are often hidden underground. This usually means some form of filtration system is required prior to the water entering the tank and a pump is used to get water out of the tank. Quite often it is used to keep a header tank topped up in the house, to provide the required water pressure. Whilst more complex to retro-fit into an existing house, if designed in from the outset rainwater harvesting makes a lot of sense and will save you a lot of money longer term.
Another advantage of under-ground storage is that water is kept cooler and has less baterial content.
Because the main water storage tank is under ground, a pump is required to fill a header tank in the home. A 'smart header tank' works on the principle that this header tank is only filled when it gets close to being empty. This means that the pump is only running once a day (for example). It could also be run at times of plentiful electricity generation.
Commercial Solutions & Suppliers
Having visited their stand at EcoBuild, we were really impressed with the quality and designs produced by Graf. Their solution has some clever innovations and covers all aspects of rainwater harvesting described above.