What a fascinating thread and way above my head on the technicalities. We have our own water supply here - and we're not alone in that, as many of the farms and smallholdings off the beaten track have boreholes, springs or wells. Ours is (I hope and pray) reliable - leastways, it was the supply to the house in Victorian times and possibly earlier than this - we merely reinstated it after a generation of it being left to its own devices.
When we brought our property it was on the understanding that the farm next door (to which this was - up until we bought it - the farmhouse) shared the water supply with us. We didn't realise that "next door" would always make sure he had the lion's share of the water and that increasing numbers of dairy cattle would run us dry. I have lost count of the number of times in the early years here when the holding tank had to be topped up with river water, so we at least were able to use it for washing and flushing the loos, and we got our drinking water in from neighbours down the hill with a more constant spring.
As someone mentioned, two dry winters have drastically reduced the amount of normal rainfall to 50 or 60%. If this carries on, we shall have to consider contingency plans, as I assume the wonderful spring which feeds our water supply, may well drop below the level where it feeds our top holding tank.
We have lost our "back up" supply (e.g. next door) already this year, as the bit between him and us has sprung a leak, so he has turned it off and we need to start negotiations on reinstating it that don't involve the cost of digging up his concrete yard (or our patio come to that!) But hey - we're all in the same boat around here, and at least our stream is still flowing, so the water level hasn't dropped too drastically yet. Neither do we have to pay water rates for a service we may not get, like those poor devils t'other side of the country . . .