water may vaporise below its boiling point then when it is heated it may also vaporise with the other substance from which it should be separated
Depending on the ratio of acetone to water you may form an azeotrope - meaning that both the acetone and water will vaporize together and ruin your distillation.
Fractional distillation might help with this.
There is also a technique called azeotropic distillation that is sometimes used to make very dry solvents. The only problem is you would end up with completely dry acetone and water that had small amounts of acetone in it.