you need to let your water authority know that you have placed a second meter in the property and that all the water passing through this is for business use but more importantly the waste is not being returned to sewer - you are either storing it and using it for pressure washing or going into the garden ( although they not look kindly to that one ) you will then NOT be charged the return to sewer on all water passing through the second meter - they may want to inspect your set up but once in place you will only need to provide readings of both meters my water charges were nearly 6K a couple of years ago as they hadn't implemented the use of the second meter - i got 50% of that returned and now we only pay for water in no sewage charges at allDarran
its stored in several ibc tanks and pumped into the pressure washing vans Darran