what causes a floor to bow up and have sink in spots if there is not a water leak?

The floors in our home we are renting has started to bow up in some places in the month and a half? we have been here since june and it started the last of july. the landlord came to look at it yesterday after being told 2 about it. he said it looked like water damage. the only thing is we haven't even seen a leak or heard one. the house is old and it only has 2 things of cynder blocks holding all the floors up. the just put new walls and stuff up in this house. we plan on moving out when we find somewhere. i just don't want him to hold our deposit just because he says it is water damage. what would be the sign of water damage if a pipe was leaking under the house say the where the washing machine is. and should he hold our deposit to fix it when we move out. could it be from not having enough support holding the house up causing it to do that.