Single tank DIR systems are typically not as efficient as systems that employ two resin tanks. In single tank units, if regeneration is necessary at a time of the day when soft water may be needed, they must wait until a more appropriate time to regenerate so hard water isn't introduced into the home. To do so, single tank DIR units must employ a reserve capacity of softening resin to make it through the rest of the day. If the reserve isn't enough, the home will be forced to use hard water until the system regenerates. If the reserve is too large, the system won't be used to capacity but regeneration will occur anyway, wasting water and regenerant.
Some systems even use soft water to clean themselves to improve efficiency.
Countercurrent regeneration also improves the systems' effectiveness. Recommended by most resin manufacturers, countercurrent regeneration regenerates the resin beads more efficiently by reversing the flow through the system during the cleaning process. Additionally, leading consumer publications including Consumers Digest have recognized that non-electric, twin tank DIR water conditioners have distinct advantages over those that operate with electricity. Water conditioners may be designed to help with other water problems, too, including the reduction of radium, barium and excess iron. In severe cases, however, a separate system may be required for proper performance.