As mentioned before call your water company.
POINTS TO REMEMBER:
Its not just the cost of the water its also the proportion they charge for waste. Ours charges just over a £1 per 1000 litres of water with an additional charge if 75% of water used for the waste (again at just ove £1 per 1000 litre) so the total cost for every 1000 litres used is £1.75 plus vat.
And on your Merlin its anything from 1:3 to 1:5 so in our area it could be costing as much a £12 per ever 1000 litres of pure water.
The waste ratio is about the same with a pump, but its quicker & has less TDS.
But as I have said many times before it all depends on the pump, you need about 7 litres per min at 80psi to push a Merlin to its max.
NOTE:7 litres per min at 80psi NOT max of 7 litres per min, max80psi Trevor only 27p per cube where do you live?
steve@freshwatersystems.co.uk