[fludlight]

That might be the cost of the water today, but history suggests that the price of water can fluctuate wildly. This is doubly true of the marginal cost beyond a certain baseline, which, again, fluctuates. Even without a drought or increase in regional population, you are vulnerable to (utility price, not CPI) inflation after ~5 years. The math for computing a break even period thus becomes squishy.

There are many people that place great value on being partially-off-the-grid, on (conspicuous) conservation, and enjoy DIY projects.

[sliverstorm]

All good points, and certainly if you went entirely off-grid, avoiding a water tap fee is big savings. Though, 110 gallons isn't going to get you very far if you're totally off-grid.