The Quero Playa Lake is an ephemeral saline playa lake located in the La Mancha region of central Spain. In this study, a daily monitoring of the brine physical properties, water activity, brine depth and main climatic parameters was simultaneously carried out together with determining the precipitation sequence of minerals. Field data were compared with the results of simulating the water evaporation in an environmental chamber. In this simulation, a similar hydrochemical composition for the saline lake was used, and the main climatic parameters, temperature and humidity, were controlled. The water balance equation for saline lakes has usually been described using the Wood and Sanford equation Econ. Geol., 85(1990) 1226–1235. Our experimental results required us to revise the water balance equation for the brine depth variations (d h/d t), that may be expressed as follows: dh dt =p 1+k A B A L +S I −S O −ξ−H+D, where p (mm) is the precipitation; k is the drainage coefficient of the lake; A L is the lake surface; A B is the drainage basin surface; S I and S O are the contribution of influent and effluent seepage to the depth of brine in the lake. The term ξ is the evaporation/condensation, defined as ξ= kp W( a W−RH), where k is the mass transfer coefficient (Dalton's equation); p W is the water pressure in equilibrium with the air; a W is the water activity of the brine; RH is the relative humidity. The other terms: H and D, correct the brine depth loss or/and gain a consequence of hydrated saline mineral precipitation and early diagenetic hydration/dehydration reactions. As a consequence of the above, we suggest that the water balance equation for saline lakes can be an important consideration in the interpretation of their evolution. The precipitation of hydrated saline minerals and the early diagenetic dehydration/hydration reactions imply changes in the d h/d t curves. As a result, the interpretation of the sequence of primary saline minerals in older evaporitic deposits may be used as a paleoenvironmental marker.