According to the Cyber-Nook website, there are a number of reasons that people use distillation units to clean their water. These units remove nitrates, chloride and salts that carbon filtration systems can't. The distillation process also kills pathogens in water. A distillation unit consistently provides quality, treated water, but it does have its disadvantages.
A distillation unit can take between two and five hours to purify one gallon of water.
Distillation units use electricity. Depending on your local rate of electricity and the amount of water you use, distilled water can easily cost more than $100 a year.
Since distillation units require electricity, they won't work when the power goes out. This can be potentially disastrous during an emergency, such as a flood or a hurricane, especially if your tap water becomes contaminated and is no longer safe to drink.
According to the Filter Water website, a distillation unit may actually concentrate contaminants with high boiling points in your distilled water. Units without gas vents, fractional columns or activated carbon filter units will leave volatile organic compounds (VOCs) behind.