Regulation of airway surface liquid (ASL) volume is one of the most important functions in lung epithelia. It is hypothesized that apical volume expansion induces activation of Na⁺ resorption via proteolytic modification of epithelial Na⁺ channels (ENaC). We aimed at adaptation of water resorption to apical volume expansion in NCI-H441 epithelia cultivated air liquid interface (ALI) using a novel deuterium oxide dilution method. Water resorption was activated not before 6 h after apical volume expansion. Apically added aprotinin and proteinase inhibitor cocktail increased water resorption by approximately 40 %. The inhibition of membrane trafficking by brefeldin A abolished water transport almost entirely. To estimate epithelial water transport capacity, cell layers were preloaded on their apical side with isotonic NaCl solution and osmotic gradients were established by manitol in the presence of 100 mM amiloride. Afterwards the osmotically induced transport rates were measured. After 1h preincubation the observed transport capacities were 50 ±6 nl/(cm²*h*mOsm) and 12 ±10 nl/(cm²*h*mOsm) for secretion and resorption respectively. Eight hour preincubation augmented solely the transport capacity for water resorption (83 ±16 nl/(cm²*h*mOsm)) but not for secretion. Ussing-chamber experiments revealed no change in amiloride sensitive I_SC between epithelia preincubated for 1h and 8h. Evidently, adaptation of epithelial transport to long-term apical volume expansion involves modulation of resorptive transport capacity rather than regulation of ENaC activity.