Potential Plumbing Problems

Last night, while we were assembling furniture (like you do), Staci noticed a water stain on the ceiling of the first floor. This spot is under the bathroom tub and hopefully its nothing too serious but we need to have it looked at. Since my skills as a plumber are none, I had to ask my dad to come over to look at it. The spanglish i came up with there was classic:

(10:52:42) Oscar: need your plumbing help en casa đŸ™‚ anoche hemos notado una water stain en el techo del primer piso. can you help me diagnose?