If you direct connect, you will need a way to cut off or bypass the supply and draw off the saved water. Since the water pressure comes from the municipal supply, you could use gravity and have a tap on the bottom of each tank, but that is inconvenient if the tanks are sitting on the basement floor. You could pressurize the reserve system (probably violating multiple municipal plumbing codes), but you would want a manual air pump in the event that electricity is off. You could also mount the tanks on a platform and tap from the bottom.

I agree with Arney that you should not routinely route your household water through your reserve supply, as all you have done is extend your available municipal water supply by 40 or 80 gallons....not enough time to react if your hear of a contamination problem.

For a small investment and in the same space, you can reserve 55 gallons of drinking water in a water barrel with a hand pump.