There are two major factors involved when comparing prices among the three modes of water purification. First, one must consider the energy needed to clean and filter water. Reverse osmosis, with its dependence upon high pressure to subvert the normal flow of water, requires an energy source and is fairly costly. Distillation, with its dependence upon heat to vaporize ground and surface water, also requires an energy source.

Though solar power remains an option for the required heat of distillation, it is still fairly inefficient and impractical. Carbon and multimedia water filters, whether installed at the point of water’s entry in a house or at a tap, do not require any added energy source. Water flows just as it normally would; it is merely diverted through the filter. The higher electricity costs of reverse osmosis and distillation systems double the total cost of the purified water product which carbon and multimedia filters produce.The second consideration one must take into account is the wastewater-to-purified water ratio. Both reverse osmosis and distillation systems are extremely wasteful and inefficient. They use large quantities of water to create a very small amount of purified water. Typically with these systems, 75-80% of the water is discarded with the contaminants. In a time when fresh water is scarce throughout the planet, these statistics are simply unacceptable. Carbon water filters waste very little of the water that flows through their systems. Due to the unique chemical and physical processes of the filtration method, only the contaminants are left behind on the filter cartridge.

When electricity use, wasted water, and replacement costs are factored into the equation, water filters generally cost about $100 less per year than reverse osmosis and distillation to generate the same amount of purified drinking water.

Source: http://www.historyofwaterfilters.com/