i would first disconect the supply line by the house or somewhere before, and as long as the cistern is full and you have primed the pump (if need be) let the water flow for a while. there is probobly alot of bugs and such living in the dried pipes. if at all possible do a pressure test on the line from the pump to the house to make sure no leaks are present. you might want to have a supply test done on the spring to make sure that it will produce enough water to supply the house.