Harvesting rainwater is a great way to provide water for irrigating your garden during dry weather or washing the car. In the UK it is legal to collect rainwater from above ground surfaces on your property (e.g. house roof, the ground). You must keep your rainwater harvesting system separate from the mains water supply to avoid contamination.
Rainwater that is harvested should be treated as non-potable, i.e. not drinking water. However, after a disaster where mains water supply is not available, harvested rainwater could also provide a drinking water supply. Do not drink harvested rainwater without purifying it first to make sure it is safe to drink.
You don’t need an expensive water collection system for harvesting rainwater. Harvesting rainwater can be as simple as a plastic barrel connected to a drain pipe. Alternatively, buy a ready made water butt to connect to your drainpipe. Below are several common mistakes that are very easy to avoid when setting up your system for harvesting rainwater.
Underestimating How Much Rainwater Be Harvested From A House Roof
A fairly small house may have a roof area of 60m2. During a month with 80mm rainfall, this roof would provide 4800 litres of water. A small container would fill up very quickly! If you have the space, several large containers would be better so that you can harvest more of the rain water.
Using An Unsuitable Container For Harvesting Rainwater
You can use almost any container for harvesting rainwater. However, unless you choose the container carefully, your harvested rainwater could be contaminated. A container for harvesting rainwater should be:
- Dark coloured and opaque: This keeps the interior of the container dark which prevents the growth of algae in the water.
- Covered: This prevents leaves and contamination falling in to the container. A covered container also prevents insects from getting inside.
- Food safe material: If you plan to use harvested rainwater for drinking after a disaster, make sure that the container is made from a food safe material, e.g. food safe plastic.
Harvesting Rainwater In A Container With No Outlet
Harvesting rainwater is useless if you don’t have an easy way to get it back out of the container. You could use a bucket to get the water from the top of the container. It would be much easier though to have a tap fitted near the bottom of the container. Buy a suitable tap fitting, and fit it just above the bottom of your rainwater container. Leaving a small gap will let any dirt in the water sink below the level of the tap so you get clean water out.
Not Cleaning Gutters
Dirty gutters mean dirty water flowing in to your rainwater container. Regularly remove leaves and dirt from your gutters so that the harvested rainwater is as clean as possible. Additionally, fit a gutter guard in the gutter at the top of the drain pipe to trap any leaves that may fall into the gutter.
Harvesting Rainwater In A Container With No Overflow
During periods of wet weather, your rainwater container will probably fill up. If your container doesn’t have an overflow system, the water will reach the top and flow over the edges. It might also push the lid off your container. Water flowing over the edges of the container may not seem like a huge issue, but over a prolonged period may cause water to collect against the wall of the house. To prevent this, fit an outlet pipe near the top of the container to direct water into another container, or to a drain. If you have room, you can connect several containers so that each overflows in to the next.