Is there a river or spring ...

Is there a river or spring at an altitude above their dwellings? If so a floating sieve intake could secure a gravity line to a settling sump tank and then down the line to a holding tank with enough gravity pressure prior to the dwelling. In NZ we would then have carbon filters prior to the home. Also sometimes when a spring source is used it may best to bury a perforated plastic culvert back-filled against with gravel and then have a floating sieve out-take prior to the first settling sump tank. Both the inlet and outlet of the settling sump tank need to be at the top of the tank and as far away as possible from each other to slow the flow and allow the greatest settlement. These are primary applications but very naturally sustainable trickle-fed systems.

In metric 1mm of rain falling on 1sq metre gathers 1 litre of water, we suggested to budget on 800mls due to mitigating factors.