There is provided an apparatus 2 for desalinating non-potable water. The apparatus has a first vapor producing module 5 configured to receive a heated working fluid for producing vapor from a volume of non-potable water for driving at least one first distillation module 10 for producing condensate 12. The apparatus also includes a second vapor producing module 14 configured to receive working fluid from the first vapor producing module 5 for producing additional vapor from a further volume of non-potable water 8′.