why is water coming out of the reseviour after it stopped running

because it over heated. It sounds like you ran straight water in your coolant. BAD move!! Water is designed to basically boil eggs / cooking aide. Anti freeze is designed to withstand heat. So the water is coming out of the res because it seeks path of least resistance ( like oil) and it wants out of the motor, and escapes under the cap and into the res. turn the valve on your radiator and drain out all that water ( providing it's just water). Turn valve off into normal position and add coolant ( 2 to 3 jugs or so ). Probably wouildn't hurt to replace the radiator cap either while you are at it. good luck