Cessna 150 pilot reported experiencing engine failure shortly after liftoff and safely landed straight ahead on the remaining runway. Post flight inspection revealed water in the fuel.

Narrative

The annual inspection had just been completed on a Cessna 150. I fueled the airplane; topping it off; before taking it on the test flight. I completed a maintenance test flight and it was satisfactory; with no problems. The next day; I flew the airplane from ZZZ1 to ZZZ; about 40 miles to the east; for an event at ZZZ. It was an uneventful flight. When I was ready to leave ZZZ; I followed my usual routine and did a walk around first; making sure the airplane was ok; before getting in and starting up. I called ZZZ ATC and got my taxi clearance to r/w XX and taxied to the run up area; and did my before takeoff check list and run-up. Everything was normal. After being cleared for takeoff; I added full power and accelerated down them runway. After taking off; when I got to about 200'; the engine suddenly started running rough and the RPM suddenly fluctuating between 500 - 700 RPM. And; right after that; the RPM suddenly dropped to ZERO and I immediately focused on landing straight ahead; since I was still over runway XX. I also had the presence of mind to quickly call the Tower and inform ATC that I had had an engine failure; and was landing straight ahead on runway XX. I do not recall what the Tower said. But I hear them tell another aircraft to go around. Presumably they were behind me; on final approach. I landed and rolled out straight ahead to the intersection of r/w XY/XZ and had enough speed left to turn left onto the inactive runway and then again onto taxiway 1; and then with what little speed I still had; slowly turned into the ramp area and stopped. At this point; the Tower called me and asked if I needed any assistance; and I told them to standby; since I did not yet know. I had to take a minute and assess the situation. This is the first time I have ever had something like this happen; in many years of flying! In spite of practicing countless emergency and abnormal scenarios; in training; it was still a surprise when it happened; for real; especially in my small single engine airplane!I was finally able to get the engine to start and run; and requested taxi back to transient parking. Then I shut down and called my mechanic. After I described what happened; he decided to drive to the airport and find out what happened. When he arrived; we took fuel samples from each tank; and the engine. We found at least a 1/2 cup of water from the engine drain; the low point in the system. I had NOT seen this previously when I checked; during my preflights. It must have remained suspended in the fuel. We continued to drain fuel to check for water until there was no more water appearing. After that; my mechanic suggested I start the engine and run it for several minutes; to make sure it was ok. I did that and then he suggested I takeoff and fly once around the pattern; which I did. It ran normally. I landed and checked with my mechanic and he said it was now ok to fly back home; which I did; uneventfully! Lessons learned. Contaminated fuel does not always show up on the first flight after fueling. Both my mechanic and I are suspicious that the fuel truck that fueled my airplane had contaminated fuel; but the driver was not aware of it. And now I will be more careful when checking the fuel tanks for water; before flying. I am submitting this report in hopes that someone else may learn from this experience; and hopefully it will not happen to someone else like it did to me. Fortunately I was still over the runway when it happened and was able to land; uneventfully; straight ahead on the remaining runway!