Going back to the OP, can I play Devil's Advocate? Consider the effect of this being a precedent. Suppose they had been granted the right to collect the water. Evil megacorp comes along, buys or rents the land and builds a huge rain collection system, depriving large areas of water. When people complain because they have to buy the water, the megacorp points to the precedent of this couple being allowed to collect the water.