Most of the west is in a continuous state of drought these days. Your tank is made from water safe plastic and can hold water for years without issue as the system is closed. Keep the water, don't dump for frivolous reasons, even cold can be accommodated. Big tanks of water have 'thermal inertia' and it takes days to freeze a large tank of water at 20 degrees in a closed compartment. Even longer if a small heater is put in the bay.
BTW, sometimes, the water in the water heater can develop a skunky, rotten egg smell. You can either drain it, flush, and treat it, or just ignore it. You don't usually drink hot water anyway. It'll go away after a few gallons have been run through the tank. The water in the main tank is usually fine.
For future reference, the following was developed by a RV'ing city water master who has a PHd in Chemistry, adjust the amounts of additives to your tank size:
Springtime Preventative: Add 1 oz bleach per 60 gallons of water
Troubled system: Add 8 oz of bleach per 60 gallons of water
To remove smells: 1 & 1/2 cup vinegar per 60 gallons of water
To sweeten water: Add 1/2 cup dissolved baking soda per 60 gallons of water.
Notice that the amount of bleach is minimal. That's all that's needed because it's that strong. Adding too much is as bad as adding too little.
