Method and device for controlling water hardness in a dwelling, comprising a water consumption circuit (17). The water supply (10) for the dwelling is first introduced into a dynamic storage device (19) and, subsequently, at the outlet of the dynamic storage device, it is introduced either into the consumption circuit (17) of the dwelling or into a purification circuit, according to the degree of hardness. The purification circuit comprises a pump (9) followed by an anti-clogging device (1) followed by an osmosis unit (2) or a filtration or ultrafiltration device. Next, the "pure water" leaving the osmosis unit or the filtration or ultrafiltration device is reintroduced into the dynamic storage device (19), while the water rejected by the osmosis unit or the filtration or ultrafiltration device is filtered and decanted in a filtration and decantation device (6) and then injected back into the purification circuit by the pump (9). Finally, the "pure water" from the dynamic storage tank (19) having a degree of hardness below a pre-determined limit value is introduced into the consumption circuit (17) of the dwelling through a mixing block such as to produce a mixture of water having a hardness of between 8°fH and 12°fH. The dynamic storage circuit (19) is formed by a pipe wound about itself into a coil and having a length equal to or greater than 10 m.