It’s allowed *because* water is scarce! Rainwater that runs off properties into the streets mostly just gets funneled away from the city and uselessly evaporates somewhere downstream, so water sinking and recharging the aquifer locally is a good thing. It also reduces the need for people to use city water for landscapes and the temporary flooding on the streets (used for drainage) during monsoon storms. Enough rain falls on the city each year to cover our needs, but we let most of it get away, which is something a lot of folks (and the city) are trying to change.
Tucson is more progressive than most places in allowing, and in commercial cases now requiring, good rainwater harvesting practices. The city actively encourages people to collect rainwater and use greywater by offering rebates for tanks
and installation/parts, respectively. In Tucson you can install a 2000 gallon (or larger!) tank if you want, and the city will give you $2000 for doing it.
Technically you’re not allowed to take water off the street and funnel it onto your property, as we did here, but that’s because of concerns that people will not do it right and end up flooding their neighbor’s yard and house. Hopefully the rules will change to make it a permitted thing. A lot of locals do it anyway already; rainwater harvesters are such rebels.
You CAN get a permit to harvest the water off the street to water trees and plants in the public right of way, so we could have created a basin parallel to the road in front of our fence instead. However, the city has a green stormwater infrastructure (GSI) grant program
for neighborhoods to get exactly that kind of stuff built, and one of our neighbors recently applied for one for our two streets. If we get the grant then hopefully we’ll see some city-funded basins along the street, with stormwater-fed trees that will provide some shade and greenery, reduce street flooding, and slow traffic.
I could talk about this for a long time but I think that’s enough for now!