I personally find it unethical to "offer" water to a family, something necessary for life, and then add the caveat that you have to do something incredibly difficult if not impossible to get that water. I would find it just as unethical if someone said "I'll pay for your water, but only if you can jump these hurdles at the speed of a high school track star!" It's not like it's the Olympics, and the person can eventually train to do that - but I would find it abhorrent to make a game out of someone's basic needs like that, you know?
For the record, last year a radio station (I know I know, bad source but not like this a difficult controlled study) went to 240 grocery stores in 6 neighborhoods in Detroit, where 30% of children in the city live. In 75% of them, you couldn't buy apples. My local Walmart has potatoes and onions in big bags and that's all it has for produce. It's not so easy in some places to go vegan.