Yes, a DI cartridge can be used as a stand-alone filter. However, the lifespan will be reduced greatly (unless your water is very low on TDS to begin with). Just refer back to the DI life section of this FAQ. Normally, a stand-alone DI is used in either lab or car washing applications. Though you can use our DI filters for these applications, we do not normally recommend it. We might refer you to a different company for DI filter units that were made specifically for these applications if we do not think that ours will last long enough for your use. Typically, you will want the mixed bed resin. However, you can use separate beds (anion and cation) as well.