A method and an apparatus for detecting whether a liquid comprising one or more improper substances or an improper amount of one or more substances has been added to a system for removing support material from and/or smoothing a surface of a part made by additive manufacturing. The apparatus may have a sample material that is altered if the improper fluid contacts the sample material. The alteration may be due to characteristics of the improper fluid at the time the improper fluid is added to the system. In some embodiments of the invention, the sample material is capable of chemically reacting with the improper fluid. The apparatus also includes a sensor capable of detecting whether the sample material has been altered.