10 days.
Assume that the average daily water consumption of a family of three is W liters. Then, 1 ton of water (i.e. 1,000 liters) can be used for 1,000/W days. We assume an average water consumption of 100 liters per day (this is only a rough estimate, actual conditions may vary). Substitute W=100 into the formula above to get the answer. The calculation result is as follows: 1 ton of water can be used for 10 days. So, 1 ton of water can be used for 10 days.