Objective: To determine the effectiveness of hydrotherapy to reduce pain, improve quality of life and physical function in adults with knee osteoarthritis, by collecting the various scientific studies of high methodological quality on the date published. Material and methods: A systematic review of fve computerized bibliographic databases was performed: PEDro and MEDLINE. We included randomized controlled trials with patients diagnosed with knee osteoarthritis trials. Articles published from January 1, 2004 to the July 31, 2014 in Spanish and English were selected. Study screening: Studies were independently selected, unblinded, by two reviewers. The PEDro scale was used to classify the studies. Results: Of the 119 studies that could potentially have been included. In determining the criteria for inclusion and exclusion only 6 items were selected for analysis. Conclusions: There is strong evidence that the use of hydrotherapy is effective in the treatment of osteoarthritis of the knee in adults over 50 years with a minimum follow up of 6 weeks.