Fig. 2: Mean diuresis (and SEM) after a water load in normal subjects and in patients with CHF and SIADH. The urine volume during diuresis is divided in two components. In the top graph, the classic osmolar clearance is the shaded area and the free-water clearance is the white area; in the bottom graph, the clearance of electrolytes is the shaded area and the effective water clearance (EWC) is the white area. Whereas the free-water clearance was positive in normal subjects, negligible in patients with CHF and negative in patients with SIADH, the EWC represented more than 80% of diuresis in both the normal subjects and the patients with CHF. The patients with SIADH did not excrete water that did not contain electrolytes.