Cessna 172 pilot reported landing safely after experiencing loss of power related to water in the fuel.

Narrative

On departure following a normal takeoff; landing gear retraction and climb to pattern altitude (800 ft. AGL) the engine began to lose power on the crosswind leg. I selected carburetor heat (though icing conditions were not likely on the day of the flight); verified the fuel mixture was rich; fuel boost pump was on; the primer was secure and the fuel valve was on 'both'. Given that I had reached pattern altitude I was confident I could safely turn downwind to return to the airport. Completing the turn to downwind it was evident that engine power would not be restored and that I would not be able to fly the pattern to land on Runway XX. I decided to land on Runway XY; configuring the airplane for landing and announcing my situation and intentions on the CTAF. Other pilots in the pattern at time responded quickly to ensure I had the runway to myself. The landing was uneventful and I was able to coast back to parking.This aircraft is rented through our local club and I was the last pilot to fly it prior to the flight described above. The previous flight had occurred approximately one month earlier. Following that flight I refueled the aircraft for the next renter but when the fuel tanks were topped off fuel began leaking from the area of the wing root and was grounded for maintenance.The aircraft is not hangared and maintenance personnel worked intermittently to assess and repair the leak over a period spanning about a month. The aircraft was located during that time on a newly-paved parking stand which slopes downward from north to south. Aircraft parked in that area park on painted tees which are oriented east to west. During this time the aircraft was oriented facing west with its left wing pointed south or downslope.During the time that the airplane was undergoing repairs to its fuel system the local region experienced storms that delivered heavy rains.While repairs were being carried out; some fuel was removed from the wing tanks and replaced upon completion of the work. The tanks were not purged following the work and no post-maintenance test flight was conducted.The incident flight was the airplane's first flight after the repairs were completed. When carrying out my pre-flight inspection and in consideration of the previous weather conditions; the fact that the airplane was outside and the fact that the fuel system had been worked on; I took two samples from each wing drain and the belly drain none of which contained any water. A note here: I mistakenly believed this aircraft was a 1981 model year example based on its airworthiness date. The 1981 POH shows a knob for actuating the strainer which; common to many Cessnas; would be located next to the oil dipstick. This knob is absent on this airplane. Nevertheless the pre-flight procedure in the 1981 manual only refers to draining the belly and wing sumps; not the strainer. Consulting the FAA database; I subsequently determined that this aircraft is a 1982 model and the pre-flight procedure for that year includes draining the strainer via a drain valve near the bottom of the cowling near the cowl flap.I mention the fact that during the pre-flight I drained the belly and wing sumps but not the strainer sump not because I believe the loss of power was caused by this action but rather to accurately describe my pre-flight actions and to note my mistake in identifying the correct model year of the aircraft and subsequent reference to the previous year's POH.Following the pre-flight inspection; the engine started normally. From engine start to loss of power the engine ran for 3/10th's of an hour. My pre-takeoff procedure included 2 engine runups- I repeated the procedure because the prop cycled slowly due to cold oil during the first runup. During both runups the engine ran normally and it produced excellent power during takeoff.Following my landing; repeated attempts to restart the engine were unsuccessful. Later; maintenance personnel drained significant amounts of water from the sumps.A Club Instructor who also assists on maintenance operations determined that water had been entering the left fuel tank through a leaky cap seal.I believe that because of the wing-low orientation of the airplane while parked during maintenance; water accumulated in the outboard portion of the tank; away from the sump drain an fuel pickup.During the taxi to runup and takeoff; changes to the airplane's attitude allowed water to migrate to the pickup and eventually reach the carburetor.Later model Cessna 172s have a larger number of fuel tank drains which seem to have been added to address the possibility that water might settle in areas of the tanks which would prevent its detection and draining in some circumstances.A friend who owns a C-172RG said that leaky fuel cap seals caused a large accumulation of water in his aircraft following rain storms. In order to purge the tanks thoroughly he spent several hours rotating the aircraft to different headings to cause the water to move to the drains; repeating the process until no water was found in the sumps. He now replaces his fuel cap seals annually regardless of their condition to be safe.In hindsight I had some concerns about flying the airplane after the fuel system repairs were completed without it having had a post-maintenance test flight conducted by the maintenance personnel or club instructors. In the future I will think twice about being the de facto test pilot.As other club members and instructors were also unaware of the cowl drain on this aircraft; a label is being placed added to call attention to it. Both fuel cap seals have been replaced.