How fast should pressure drop?

Assuming no leaks...

If I hit about 5 gallons of uncarbonated water with 18-20psi for a couple minutes, and then shut the CO2 off - how long should it take the water to absorb the carbonation (constant temperature) and the gauge on the regulator to hit zero?

I did this last night, and about 24 hours later it's at 8psi - so I'm trying to figure out if I have a leak. I sprayed all the connections down but saw no leaks yesterday.

I don't have the answer to your question, but have to wonder why you would shut off the CO2 after a couple of minutes?

The pressure in the head space will drop as CO2 is absorbed into the beer until it reaches equilibrium. It should never hit zero. Your beer won't fully carb if you shut off the gas.

Set it at serving pressure (10-12 PSI for an average ale), leave the gas on and it'll carb in a week or so.




edit:
Just saw it's water in you keg. Making seltzer?
But the same thing applies for water or beer about dropping pressure until equilibrium is reached.

If all you're doing is checking your kegging gear for leaks, get rid of the fluids, just use gas, and spray every connection with something that will bubble up on a leak (soap/water, standard Star San mix, store-bought leak finder solution, etc)...

Cheers!