The dimensions are standard for what is known as a 50 Gallon (230 Litre) Cold Water Storage Tank. Although having a physically larger capacity, this will be the working capacity as they are not intended to be filled to the brim as room is needed for the float valve and overflow connections as well as allowing some space for expansion when they are installed to feed hot water systems.
As has been previously said, it's probably because of the size of your property and the possible maximum demand for water. If you have several bathrooms / WC's, or power showers, then it's likely one tank will feed the hot water system and the other provide a cold supply for the bathrooms and WC's.
The smaller tank will be about 4 gallons. They are used to provide a cold feed to a boiler / radiators and to allow space for expansion of the water in the system as it heats up.
As has been previously said, it's probably because of the size of your property and the possible maximum demand for water. If you have several bathrooms / WC's, or power showers, then it's likely one tank will feed the hot water system and the other provide a cold supply for the bathrooms and WC's.
The smaller tank will be about 4 gallons. They are used to provide a cold feed to a boiler / radiators and to allow space for expansion of the water in the system as it heats up.
