The lack of water pressure « not connected to the public network » is a major disadvantage. For very small areas, it is not too much trouble to fill a bucket or watering can at the tap of a tank, in a bin or a well. Beyond that, it is necessary to equip yourself with a thermal or electric pressure pump capable of sending water into the pipes with sufficient flow and pressure. These solutions are not always very happy: noise, fragility, impossibility to repair, dependence on an energy source, costly renewal. By using gravity, i. e. by storing water at a height (water towers, 1 m = 0.1 bar), the necessary pressure can be created without a machine or it reduces its power and therefore its cost.