Greywater system

Today we finalised the greywater system that we are going to install . It is a very basic setup , greywater from the bath and the washing machine goes in a subterranean tank with a submersible pump which pumps it up to the terrace . The contractor is going to do the job of pumping up the terrace and I will make the rest of the filtration system which is essentially going to be a trench with gravel . The water will be released into a subsurface drip system . Schematically it is going to be like this .
If the water pump is 0.5 kw and takes even as much as half an hour everyday to pump up the water , the monthly consumption of electricity will be 15 Kwh which at 0.50 shekels/Kwh works out to 7.50 shekels a month or less than 2$ a month . The water saved will definitely offset the cost of running the pump .