The global-warming virtues of composting were confirmed by none other than InSinkErator. They commissioned a study of sewage-treatment and food-waste-disposal methods and found that while some super-efficient sewage treatment plants eliminate greenhouse gas emissions while producing surplus energy, few systems beat composting—even when factoring in the emissions from hauling away and processing curbside compost.
However, if you can’t compost (vegetable, fruit and plant based waste) use the in-sink disposal. The amount of water needed to deal with in-sink disposal is negligible and controllable in the big scheme of things. The worst method is tossing food waste in the garbage. Landfilling (which includes hauling) releases almost twice as much global-warming gas as treating sewage and six times more than composting. U.S. residents dump 34.6 million tons of food waste annually into landfills, which accounts for almost one-fifth of all U.S. methane emissions.