A best evidence topic in thoracic surgery was written according to a structured protocol. The question addressed was: 'is water washout more effective than normal saline washout after lobectomy in preventing local recurrence?' Altogether more than 48 papers were found using the reported search, of which nine represented the best evidence to answer the clinical question. The authors, journal, date, country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. Tumour cell 'spillage' after cancer resection is linked to a worse prognosis, so washout to minimize contamination is an established surgical technique. While the mechanical effects of lavage are well validated, the differential cytocidal effects of water versus saline as irrigation fluids are not. There are currently no studies addressing this issue in the thoracic surgery setting, after lung cancer lobectomy. However, the majority of relevant papers describe the use of basic in vitro methods and animal models to produce data that can conceivably be extrapolated to the clinical question in hand. The number of studies is small, and some have technical limitations. While two of the better-designed experiments suggest that water exerts a superior cytocidal effect on tumour cells, data from other studies are somewhat unimpressive, with two studies reporting that water washout controls tumour growth to a lesser extent than saline. This, together with the complete paucity of clinical trials on the subject, leads us to conclude that water is unlikely to represent a superior irrigation fluid in lung cancer patients after lobectomy.