Don't try this at home.
Last night, Shauna and I were baffled by a lack of water pressure throughout the house. Fearing the worst, I ran downstairs to check the main only to find no sign of leaks. I couldn't find any obvious sources of water, so I called the water district and we went to bed.
This morning, the water guy came out and found the source of the leak: a burst pipe for the sprinkler system. The pipe probably froze some time ago and just now thawed with the warmer weather we've been getting. Apparently Dopey McNumbskull (that's me) had no idea that you find and turn off a special valve just before winter to make sure that kind of thing doesn't happen. I'll add that to the list of "things we must repair by late April but don't really have the money for."
A house really should come with an owner's manual for us n00bs.