If you have the space on your dirt, there is nothing wrong with a good old fashioned galvanized steel tank. You can put a lot of gallons on a little bit of space. If you continually circulate or flush the tank by using it for lawn watering or other use, and feed it with a trickle feed from a well of a float valve on muni system, it is always fresh, and always there. You just have to decide how tall you want it to be. 4' in diameter is a lot of water at 6' high. 80 cubic feet is how many gallons?