Click on the TV above to watch a Graf video on rainwater harvesting
New video showing assembly of a Graf Carat tank

Download our fitting instructions for the Carat system

Rainwater Harvesting For Farmers

The Environment Agency has issued an excellent new publication 
- Rainwater Harvesting: an on-farm guide

Payback for rainwater recycling tank and equipment in just 2 years

Farmers and Agricultural Contractors why not take the example in Environment Agency Rainwater Harvesting and On Farm Guide (2009) page 14, and use the approved tank size calculator which you can find on the web here 

Demand
200 cows in the herd drinking 84 litres per day makes a demand of 6.132 million litres or 6.132 cubic metres of water a year

Supply
The roof area in the example is 3,000 square metres in a region of the UK where rainfall across the year is 700 millimetres. After 80% filter and evaporation loss (British Standard 8515) this roof will supply 1.68 million litres or 1,680 cubic metres of water a year. This is the same as an average of 4,600 litres per day.

Balancing supply and demand
The yield of the roof is not enough for drinking water for all the cows, in fact only 27% of what’s needed. But that is still mains water saved. In fact, if the demand is bigger than the supply, the tank size can be smaller because it will be emptied faster and will more often be empty to receive a new rain shower. In the EA example, this roof would give enough water for milk cooling or parlour washing. By the way, who says you can’t store the water used for milk cooling (a bit warm) and use it for floor washing later.

Payback
The tank size calculator and the standards used indicate a tank size of 96,600 litres, enough to hold the average daily supply off the roof of 4,600. 21 times 4,600 makes 96,600. The retail price of a 21,000 gallon (95,000 litre) corrugated steel tank is £2294 ex VAT. With delivery charges, fitting, filter and pump that would come to more like £3000.

The savings are 1,680 cubic metres of water a year @ £1 per cubic metre (www.water.org.uk) which makes £1,680 i.e. payback of £3000 in just 2 years (3000 divided by 1680). Payback would be even shorter after financial incentives under DEFRA’s Farming and Forestry Improvement Scheme.

> Download the Environment Agency Rainwater Harvesting and On Farm Guide (2009)

This scheme has closed but read more here> Rural Development Programme for England - Farming and Forestry Improvement Scheme (FFIS)

01733 405111
 

Home