5th Stage - Mixed ion exchange bed deionizing filter which makes the water suitable for autoclave systems and laboratory applications. 5th Stage filter for the 5 stage purification system. Option 1 - Carbon filter (WLP6) for final finishing of water prior to dispensing Option 2 - Mineral filter (WLP13) helps add back minerals to the purified water prior to dispensing Option 3 - Granular Activated Carbon (GAC) and alkaline filter (WLP12) finishes the purified water and changes the pH value from acidic (the pH of purified water is normally 6.5 depending upon the pH of the supply water) to alkaline with a pH of approximately 8.5 depending upon the pH of the supply water. Option 4 - Mixed ion exchange bed deionizing filter which makes the water suitable for autoclave systems and laboratory applications.