Your neighbor is half right but he's pointing at the wrong thing. The big hidden cost with gravel isn't the diesel from hauling it and it isn't the water either, it's the heat. Bare rock and gravel soak up sun all day and radiate it back at night, so your yard gets hotter, which makes your house work harder to stay cool, and that's where the real energy gets burned. Grass actually stays cooler because it holds moisture and shades the soil. So you didn't move your water use somewhere else, you traded a little water for a lot of heat. If you want rock to actually pay off, put some shade trees or big native shrubs in with it so the ground isn't just baking. The weed spraying thing is on him though, you can pull weeds by hand or use a vinegar mix and skip the sprayer.

Saved his $400 X-Men run with a hair dryer, but was any of it actually valuable or just a complete run?