What you need:
Have a water flow
A cup (bucket)
A BIG jug (backup)
Something to use the water (mouth, shower, sink, etc...)
Use the water as you normally do, but also put a portion of the water in the cup and the jug.
If the cup is full, put it into the water flow.
If the water suddenly runs out, no worries, put the jug in the water flow and things will be fun and games again.
If there's no water in the jug anymore, put the cup in for a really short using session.
If you are really desperate, use the drops from the water flow, cup and jug.
Program