"One inch of water"

[jeff47]

7. Do you have a water meter on your hose?

How, exactly, do you measure acre-feet or even gallons that your hose puts out?

The actual volume your hose puts out will depend on the water pressure at your house, which is not uniform throughout the country. Heck, it isn't uniform throughout a single neighborhood. You could even get different flow rates from different faucets on your house - back when we built houses, we'd regularly put a faucet or two in front of the pressure reducer.

As a result, any measure in volume either requires spending a lot of money for a water meter, or it requires measurements as I described.

Since nobody's going to buy a water meter, they're going to use those measurement methods. Labeling it "an inch of water" takes one step out of the calculations - you don't have to figure out how many gallons it takes to cover the relevant area in 1" of water.