In the vivarium water quality is of the utmost importance. Normal tap-water contains too much lime and other soluble salts. When this water evaporates these salts will remain in the system and their concentration will rise dramatically after a period of time. Plants like orchids and ferns which normally receive pure rain water can not endure these high concentrations and will eventually start to die off.
Pure water contains neither lime nor salts.
If the vivarium is filled with pure water, high concentrations of soluble salts will not occur and all plants will thrive. This system consists of a tube containing resin granules, which are charged positively and negatively. The soluted ions are absorbed by the charged resin and the filtered water will be free from all soluble salts. After some time the granules become saturated and have to be replaced. As an indication the resin will change colour from blue to yellow.