PVC Pipe as a tank

I was deciding how to store water without taking too much space a thought it would be a good idea if I used 3"-4" pvc pipe as a water storage tank. I would use the lead-safe pvc so we could drink it if needed. And I figure with some 90's I could get about 2 10ft of lengths inside my frame. That would be over 20 gallons or so.
Also, I thought about pumping air into the pipe (not much, maybe 20psi or so) to get it pressurized then I wouldn't need a water pump. 12v air compressors are pretty cheap. Any thoughts? Concerns?
Also, I thought about pumping air into the pipe (not much, maybe 20psi or so) to get it pressurized then I wouldn't need a water pump. 12v air compressors are pretty cheap. Any thoughts? Concerns?