How do you get the water out of the heater if there’s no water pressure?
Gravity.
If you are on city water, shut the outside water feed valve off to eliminate any possibility of water from your house draining back into the distribution system as the pressure drops.
Open a faucet and leave it open, preferably one on a second floor if you have one. This will prevent a vacuum lock by letting air in the system as you drain water out.
Drain the water from the water heater through the drain valve on the bottom of the heater.
If there is some sediment in the water just filter it out before drinking the water.
Paper coffee filters do a good job of filtering water.