Depends on your family water usage , just check your water bill reading and divide them by 60 days.You can get an accurate how much water you use perday during mco.

Second , get a water stainless steel tank that can be 2 dual installation which can install at ground floor and root suggested by jetblast.Get a better pump

Install at ground and if you know DIY , save much more.

3rd , Buy a water splitter for steel tank.Not too sure what it is call.Example , if there is no water disruption ,you can switch back to direct water pipe manually.So you'll avoid using the tank regularly for a year until need to wash and can be empty then tank when you want to use the tank water manually.

If you don't have the space , by 2 tanks with 1 install at the front another 1 backyard.Split to 2 x 600 liter.As most, it'll be temp for 3 days to a week.

If really urgent , buy a 2 x 600 liter , DIY and install the vase , rent a lorry , go any shop which allow you to fill up those tank and bring back home.So you can use the water immediately .