What is the difference between the WaterWise 4000 and the WaterWise 9000? They look like they do the same thing?

Basically the 4000 distiller is faster than the 9000. The 4000 is the "age old" design, while the 9000 is sleek, and "new" design. The 9000 has a stainless steel boiler, with plastic sides, whereas the 4000 has a stainless steel boiler, and sides. The 9000 water container is self contained in the unit, and the 4000 it is separate. The 4000 has a smaller post carbon filter, that probably needs to be replaced sooner than the 9000's. (Although the filters are much cheaper)

The other differences between their two water distillers other than the obvious change in styling has to to with the 9000's longer lasting heavier duty nature. Though it actually treats water at a slightly slower rate it is designed to produce 3 gallons of distilled water a day for roughly seven years whereas the 4000 is good for approx. 2 gallons a day for two to three years. Though either machine is generally easily repaired at the end of it's life cycle and unlike other filtration systems the distillation process does not become less efficient as the parts age.