DI versus RODI: Which Do I Need?

The initial cost of a DI tank is quite a bit less than an RODI system. DI resin is expensive, which is why and RODI tank may pay off in the long run.

With an RODI system, the water first runs through an RO filter, removing about 98% of the water's impurities. Then the rest of the water goes through a DI filter, greatly reducing the amount and cost of DI resin in the long run.

RO membranes can last quite awhile, especially is the water first runs through a pre-filter. This is a carbon and/or sediment filter that water runs through before reaching the RO filter. So when you hear the term "3-phase system," it's referring to a system with a pre-filter, then an RO filter, and finally a DI filter.

When choosing whether you need a DI tank versus an RO/DI tank, there are a couple of things to consider.

1. What is the average TDS of the water you’re working with? If your water is measuring at 150 TDS or higher, you’re probably going to be better off with an RO/DI system. Using RO not only filters better, it reduces the amount of DI resin needed.

2. How often will you be cleaning with pure water? If you’re only cleaning with a water fed pole once or twice per week, then you may be able to get by with a DI system alone, like the Unger Hydro Power Ultra, even if your TDS is higher than 150. If you’re going to be cleaning daily, however, an RO/DI is probably a more cost-effective option.

When choosing an RO//DI system, there are different models for different amounts of work. For example, we like the Pro Tool Eco Cart as an entry-level or residential RODI system. The Eco Cart 3-stage RODI cart is the best pure water bang-for-your-buck system out there.