water pressure from water cache barrels...

[Timelord]

My grandfather does just that with his toilet system. He is a Yorkshireman after all! If you connected even a few of those large elevated barrels to the whole of the house water system, you would run out of water pretty soon. The general water system of a house uses quite a lot of water - or should we say, the inhabitants do, when the facility is available. It may be best if you ran a hosepipe from the barrels into the house and had a tap fixed at the end. Preferably with a filtration system inline if you were going to use it for consumption. Then you could easily control & monitor the usage. simple stuff & cheap to do.