Stage 4 – Deionization Cartridge for the Sterisil AC+ Autoclave Water System Stage 4 Cartridge readings are based on the quality of water coming off them. As incoming water can vary over time, users should consult the onboard monitoring and alerts for real-time status and replacement intervals appropriate for their environment. Water quality readings can be found on the far right monitor on the AC+ System. *Dispose of cartridges into regular trash.