To cut a long story short: New bathroom in upper storey of 2 storey extension. Been in a few months, all fine. Last week I noticed a puddle of water on the floor after having a shower. Didn't think too much of it, assumed it was a splash, mopped up, carried on. Noticed it again the next day after shower and again the day after so did some investigating and it is coming up from the gap between the vinyl tiles. This is only when the shower is in so I can only assume they is a leak in the pipe that takes the water into the main downpipe. Spoke to builder who refuses to believe me and says it must be the shower tray overflowing or a blockage. I don't see how a blockage could cause water to come up through the floor, surely it just wouldn't drain away in the first place? He's saying because there was no water showing through the ceiling of the room below it can't be a leaking pipe /drain. In fact there was, a few hours after the last time, a thin line of damp on the kitchen ceiling which corresponded with the site of the puddle above. But it dried out quickly so in assuming again this is shower drainage related as it's only when shower is running that the problem occurs. Just wondering if there is anything I can try to ascertain what's going on? Could it be a blockage? The shower doesn't drain that quickly but I am pretty certain it's not overflowing. Shall I buy a plunger 
?