Ensuring water line is shutoff

[DIYSAM]

I’m wanting to replace the single handle cartridge on my basement shower since it no longer allows hot water (sink in same bathroom works fine). I have turn off the water main (at the sidewalk), cold water intake to water heater and opened up all other faucets in the house. However, the shower spigot keeps dripping water at a rate of about 1 drop per second. If I turn the faucet off the dripping stops. Once turned back on the dripping continues. No other faucet in the house is dripping.