Objective: Most anti cancer drugs kill cancer cells by inducing programmed cell death which is a fundamental biological mechanism characterized by programmed activation of specific biochemical pathways leading to elimination of unwanted or damaged cells. An important aspect of apoptosis is an redistribution of intracellular ions and water, a process known as AVD (apoptotic volume decrease), which is seen during the initial and execution phases of apoptosis and suggested to be important for control of apoptosis. Regulated water transport occurs via plasma membrane proteins known as aquaporins (AQPs). To study the role water transport in cisplatin-induced apoptosis we developed an aquaporin (AQP) KO culture model based on Ehrlich ascites tumor cells (EATC). Methods Wild type EATCs (wt-EATC) express mRNA transcripts for AQP5, AQP3 and AQP9, AQP5 being elevated about 60-fold. Stable EAT cell clones with AQP5 micro RNAi knockdown (miR-AQP5) were generated and selected based on AQP5 protein expression. Rescue was achieved by reintroduction of an AQP5 mutant immune to the AQP5 micro RNAi into miR-AQP5 cells. Results: Compared to wt-EATC, steady state growth rate in miR-AQP5 was reduced while caspase 3 activity was unchanged. Treatment of wt-EATC with 5 mM cisplatin for 20 h induced an AVD-response and a 3-fold increased caspase 3 activity. In miR-AQP5 the AVD response was unaltered compared to wt EATC but caspase 3 activity was suppressed by almost 60%. Reintroduction of AQP5 in miR-AQP5 cells partially restored sensitivity towards cisplatin by increasing caspase 3 activity by 50%. Conclusion: Thus, AQP5 play an important role in the progression of cisplatin-induced apoptosis in a process independent of changes in AVD.