Unless you are a farmer or an engineer in that field or something to do with irrigation planning, how can you have an informed opinion on this?

What do you mean by that? Do you mean, say, not watering your lawn between noon and 6PM or similar? That makes sense as its the hottest time of day so your watering has minimal effect. If you mean irrigation in the agricultural sense, I hope you don't like eating as if that becomes an illegal practice we're going to run out of food quick.

Prediction.
Water and who owns it, across boundaries,
will start a major war in the next 10 years.

if you mean not being able to water anytime you like with no restrictions .. well we have had this in Australia for a number of years and its no big deal... things like only being able to water on certain days between certain hours and not washing your car with a hose and not hosing down hard surfaces, you get use to it and it DOES save a shit load of water