Water supply is a chain of functions
A running tap requires a source, delivery, pressure, suitable quality and a route for wastewater. A well may stop supplying water without electricity; a storage tank may still need a pressure system. Consider drinking, household and irrigation needs separately because quality requirements and acceptable interruption periods can differ. Calling a source independent does not establish continuity at every fixture.
Stored quantity does not establish quality
Tank volume describes quantity, not fitness for use. Container materials, contamination protection, turnover and cleaning access all matter. Water composition needs appropriate testing; a domestic filter is not a universal treatment for every source. Do not copy another property's treatment arrangement without information about your own water. The storage and treatment strategy should be considered together.
Match the pump to its reserve supply
Electrical backup must account for pump starting, duty cycle and controls. Frequent short cycling and running without water are different undesirable conditions that the design should address. Usable water in a pressure vessel is not equal to the vessel's full geometric volume. Pressure settings, usable reserve and pump compatibility depend on the selected system rather than on tank size alone.
Include wastewater and maintenance
Independent water delivery does not remove the electrical and service needs of pumped drainage or treatment equipment. Review simultaneous loss of water and electricity, valve access and leak detection. For an initial discussion, provide the source type, available water analysis, household occupancy and drainage arrangement. Tie stored volume to the functions and interruption period that must be covered. This exposes dependencies that a tank-and-pump shopping list would leave unresolved.