Once you master the technique you"ll save loads of water.
I don't tend to think of how many houses I can do with my water, more like how much many I can make with it.
So with my 400 litre tank I aim for around £150 plus a day, whether that be 15 £10 houses or 5 £30 houses.
Once you master it you"ll know roughly how much you can earn in a day with how much water you have.
The right setup is also critical ie brush, pole, water saving devices to how much you can handle, not just the size of your water tank.