As a good prepper, I bought myself a couple of spare water heaters several years ago (actually by accident). I installed one, as my original was getting old, but I still have another brand new one.
I’m good for close to 20 years before being forced to buy one of these dogs.
It just can't hold it at 40 psi.
I know because I took mine apart when it went, and I couldn't get it to leak after I filled it with the garden hose. Might be a good pre-heater/water holder in general.
I'll have to examine it more this summer.