Lawns use ridiculous amounts of water for zero agricultural productivity.

No, they don’t. The vast majority of water is used for agricultural and industrial purposes.

Even if you completely eliminated lawns, you wouldn’t make a meaningful dent in water consumption.

https://blogs.scientificamerican.com/anthropology-in-practic... says "Lawns are the most grown crop in the U.S." - would be interesting to see more detailed data on that.

The vast majority of lawns don’t get watered aside from the rain.

That's not the case at all in California. There's thousands upon thousands of lawns and most people water them all year. Many cities still have ordinances requiring lawns be maintained, you can't just let them die or go to weeds lest you be fined. It's expensive to convert them to drought tolerant landscaping so most people just keep grass lawns. HOAs are militant about lawn maintenance and often restrict how lawns can be redeveloped from grass.

It's only in the past decade or so new development has started requiring drought tolerant landscaping. Municipalities have also recently introduced ordinances to limit watering. But this is all a reaction to the serious droughts we've had rather than being proactive.

And yet total residential usage of water is only 10% California’s residential / agricultural / industrial water usage. Agriculture is 80%.

The grass bandaids on commercial lots is not captured by that 10% residential use figure. So all those dumb strips of grass on medians and in front of strip malls get counted in that 80% figure. A lot of that water is wasted by running off into drains.

Grass lawns are a waste of water, gas (mowing/maintenance), time, and effort. Reducing grass lawns in residential and commercial spaces would make for a meaningful reduction in the state's water usage with little reduction in economic output.

No, the 80% figure only includes agriculture. Not grass fields on commercial lots. Consider this: produce is mostly water. Now consider the weight of all the produce in California (including waste like corn stalks or potato plants) to the weight of all the grass lawns. 8:1 would be an extremely generous ratio in favor of the lawns.

This has some merit in the mountain west, but back east nobody waters their lawn, it just comes from the sky for free. (I know some people have sprinklers, but having grown up in Chicago, I can tell you that they're not strictly necessary.)

Chicago lawn here. As a point of principle I don't water the lawn. It sometimes goes dormant for a bit in the summer - I don't mind the yellow look since the park is yellow and it feels like it fits the general hot, dry spell - but springs back to lush and green once the rains come again.

Unless that water makes it to a street drain, it’s a 100% renewable resource.

When that water evaporates, it goes up in the air, and then falls back down as water.

The contention is that the usage of groundwater removes it from the ground, which has long lasting effects. Long term overuse of groundwater has caused some serious problems. It's of little use to us in the sky anyhow.

Ah yeah, don’t pump your ground water for agriculture, doesn’t matter if you’re dumping it on almonds or grass. I’m well aligned on that.

But water is not a scarce resource and putting it on plants is not a negative sum game.

The planet recycles water. Grass is 100% sustainable if maintained using the planets natural water cycles.

The water in the sky falls on a water shed which is harvested into a local water supply which comes right back to a tap.

Very important to append: when they are irrigated.

Not everywhere irrigates their lawns.

But I agree with the sentiment. The amount of energy I see in the US being put into maintaining an artificial environment in places that otherwise would be barren is astounding.

uh, have you never been to a park? that isn't irrigated and looks fine.

The land use change is a bigger factor than the mowing. Though you're right, we should work on reducing lawns and car usage.