Water is leaking through my ceilings, what could that be?

It really depends on when you started noticing the water marks on the ceilings. If it happened just after a winter freeze, it could be water pipes or anything else. But quite often if it seems like there is no reason, it could be that the “catch tray” of our airconditioning system has overflowed for a while and as such has rusted and now the water is seeping through the rust and falling onto the ceiling. It is best you get a home inspector as soon as possible to assess the damage and help you with information that could prevent further damage.