Businesses can determine their need for rainwater harvesting by assessing their water usage bills. It is also beneficial to assess how much water on the premises is used for potable activities and how much for non-potable activities.

STEP 1: Quantify the amount of water you currently use.

This can be done by checking recent water bills. It would also be useful to create a spreadsheet to record your water consumption for different seasons of the year. This will allow you to see the effect rainwater harvesting is likely to have on your costs.

STEP 2: Quantify the maximum water you can harvest in a year.

This can be done by using the following equation:

                         Y = P x A x 0.8

                         Y = Annual rainwater yield in m³
                         P = Annual percipitation in m
                         A = Collection area in m²

0.8 = Typically you should expect to collect 80% of this rainwater each year due to losses in filtering and small rainfalls that do not generate enough runoff.



STEP 3: Check your water bills to find out how much you pay for water and how much you could save by using by using rainwater instead.