With mains water costs rising at 4% above inflation more farmers are turning to barn and shed roofs to make savings on their water bills. some rainwater harvesting manufacturers claim that their systems can recover up to 40% of a farm’s water usage.
Rainwater harvesting is simply collecting rain which falls on roofs, then storing it and using it as a resource. The information below is extracted from the Environment Agency’s Rainwater Harvesting on farm guide which can be downloaded in full here.
On farm rainwater harvesting
- There are many different systems but they all have the same features that include:
- Water is collected from barn roofs and filtered and then stored
- Each square metre of roof represents a cost saving of between £1.50 and £4.50 per square metre
- Water is pumped or piped directly to the point of use or to an internal break tank
- If the system runs low on rainwater, a mains or other back up will guarantee continuous supply
- When it rains again, the system changes automatically back to prioritise the use of rainwater
- Reduction in mains water supply costs
- Reduction in sewerage costs
- Reduction in the amount of water entering a slurry store
- No treatment additives present such as chlorine and therefore is considered by some to be better for irrigation
- Avoided site drainage and flood risk
- Potential reduction on supply from rivers and ground water
- Potential contamination from bird/vermin droppings entering the store is perhaps the biggest risk
If water is only to be used for yard wash down this may not be an issue
- Filtration/treatment is recommended for drinking water or if used for dairy plant cleaning; this will add to the capital costs, but not significantly
- Water storage will typically be the largest cost
- Finding a site for a tank, pond or lagoon can be an issue on existing units
- Running costs: there will be some running costs for pumps, filters etc but this will be modest if spread over sufficient volume of collected water
- Don’t forget the hidden disposal cost from excessive water use. Collected roof water is often regarded as ‘free’ however the cost per m3 of harvested water will be significantly less than mains supply, but not ‘free’
- More importantly, the cost of disposal of dirty water can be significantly more expensive than the cost of water purchased from a water company. So, if harvested water is used excessively, for example for parlour wash down or plate cooling (without re-use), then the cost of dirty water disposal must also be taken into account
- How much water is used and what is it used for?
- How efficiently is water being used?
- Is there enough rainfall?
- How do I calculate potential collectable rainfall?
- What quality of water do I need for activities such as crop irrigation and animal drinking?
- How am I going to store the collected water? (as water storage is potentially a significant cost)
If you are using harvested rainwater for hand, udder, or dairy plant washing, or for irrigation, you need to contact the Local Authority since an Environmental Health Officer will need to assess the water annually. If the overflow water from your harvesting system is being discharged into a watercourse you need to inform the Environment Agency
If you are discharging clean overflow water into surface water drains, then this is permitted but only if it is uncontaminated. If you are discharging any contaminated water into a foul sewer you will need to contact your Local Sewerage Company.
If you are considering alterations to existing buildings or putting up new structures, you will need to contact your local planning authority
Adapted from the Environment Agency Publication “Rainwater Harvesting – an on farm guide“
Considering installing a rainwater harvesting system? Click here to download an interactive calculator to calculate potential water that you could collect from your building’s roof. Interesting in installing a rainwater harvesting system. Click here to read the experience of a Devon winemaker on capturing rainwater and using it in his winery.