A simple water balance model was used to calculate soil water reserve in a Mediterranean forested catchment. The relationship between soil water reserve and leaf water potential and stem water content was analysed. The usefulness of these variables as plant water status indicators was tested. The analyses were developed with a seven-year-long database (2001–2007) in the case of soil water content and with a four-year long one (2004–2007) for the tree variables. The soil water reserve showed similar types of behaviour for every year, with minimum values at the end of summer (75.2 mm in September 2003) and maxima in winter (204.7 mm in January 2001). The balance model built with precipitation, runoff and ETo simulated the soil moisture content well (r2 = 0.85, p < 0.001). Seasonal variations in the tree variables followed a typical trend, maximum values (−0.18 MPa in June 2007 and 0.654 cm3 cm−3 in May 2004, respectively) being observed at the end of spring, and minimums due to summer drought (−1.5 MPa and 0.520 cm3 cm−3 in August 2005). The relationship was stronger between soil water reserve and stem water content (r2 = 0.85) than with leaf water potential (r2 = 0.67), suggesting stem water content is a more sensitive indicator of water limitation.