How do I kill mold forming permanently?

My house is very damp and the mold is persistent.I have tried bleach which cures the problem temporarily.I have tried a tea tree concoction which got rid of the damp smell but apart from bleaching and constantly decorating how do you get rid of this mold. It is horrendous.I have just bought a dehumidifier and it is taking 2 tanks full of water per day even after a month.I am getting to the end of my tether. Help anybody?