To add to your answer. Yes, lawns waste water. They also require fuel burning machinery to maintain, causing pollution. And then there are the chemicals (fertilizers, weed killers, insect control, etc.). Go back one more layer and you have the sod farms which use water, fuel, chemicals, etc. And I am sure the chain continues for another layer or two.
All of what you add is entirely optional. It is possible to keep a "nice lawn" around your house, without use of fuel and chemicals. Water however is mandatory if it's not raining enough.
Water is not mandatory at all. Grass with a healthy, deep root system will survive extended droughts just fine. It just turns brown and people don't like that.
That was the point. You need water to have green grass in dry climates - all the others are optional.
Everything under discussion is equally optional. You need water to have green grass just like you need to mow the lawn to have short grass. Neither of those things are required by the grass, they are purely optional things society expects of us.
Though if your grass is both long and dry, that presents a bit of a fire hazard.
I get a nice mix in Indiana. In the spring the lawn is green and thick. I have to mow it once a week. In the summer the lack of water slows and eventually stops the growth. After early July, I mow only one more time the rest of the year. Copious shade overhead keeps it from getting too terribly brown. In this situation the grass is less work than anything else I can think of other than letting trees and bushes go wild across every square foot. I like the open space. It takes about 2 gallons of gas a year for a double lot in the city.