All Nuaire Water Jacketed Incubators should only be filled or topped off with Single Distilled water, NO PURER THAN 1 MEGAOHM. Absolutely NO Chlorinated or Halogen Material is to be used in the water Jacket. Other then Single Distilled water (no purer then 1 mega ohm), no additives need be added to the water jacket. Copper Sulfate is formed in the water jacket when the single distilled water and the unit’s internal copper tubing come in contact with each other. If still concerned, a small amount of Copper Sulfate may be added to the water jacket.