Choosing between a DI and an RO/DI System can be confusing, especially if you are new to water fed window cleaning. You might ask, why are there different types of systems? Why can the costs vary so much? Which one is right for my area and my jobs? We’re here to break it down in simple terms, starting with the most important factor, TDS.

TDS

First, let’s explain what TDS is because that is the main factor in deciding between these two systems. TDS (Total Dissolved Solids) indicates if you have hard water or soft water. Hard water is anything over 100 ppm and Soft water is under 100 ppm. You can use our TDS calculator if you’d like to see the averages of what’s in your area. The water quality varies across the country based on the amount of minerals and particles in the water. Calcium and magnesium are good examples of what we don’t want to leave on windows after washing. After you purchase your system, you’ll want to keep a TDS meter on hand to test the water coming out of your system on every job. 

DI Systems

Water passes through DI Resin beads that pull the contaminants out of the water through Deionization. Those undesirable elements in the water stick to the resin beads and pure water flows out of the tank. Sometimes these systems will have a pre-filter on them to help trap the larger particles. Primarily these units rely on only one stage of filtration. Because water only has to pass through one filter, they are able to maintain great flow from the source. 

These DI Systems are very affordable to get into, however, once the TDS starts to rise, you have to replace all the resin. A half cubic foot DI tank costs $139 to refill (at the time of writing). The time the resin will last depends on the quality of the water entering the tank. The higher the incoming TDS, the faster the resin will be exhausted. There are some areas, like Georgia, where the water is extremely soft to start with so the DI resin barely has any work to do and will last a very long time. 

PROS:

• Affordable to purchase

• Easy to Maintain

• Good Flow

CONS:

• Not suitable for TDS over 100

• Expensive to refill

• Cannot use with a booster pump

RO/DI Systems

Multi-stage systems utilize a variety of filters in order to create pure water. Depending on the system, there could be one or two pre-filters that are carbon, sediment, or Chloramine filters. These are around $10 - $20 to replace and should be swapped out every 1 - 2 months. The most important part of these systems are the RO Membranes. These filters last 1 - 2 years, when treated right, and cost around $399 to replace. They remove 90 - 95% of the minerals in the water. The DI cartridge in the system is what removes the last little bit to get your TDS under 10 ppm for spotless windows. 

These systems are harder to maintain because of all the filters and they produce less flow than DI only systems. The initial cost is more expensive than a DI unit, but they are cheaper to maintain overall. You also have to be mindful to keep water moving through these filters regularly so bacteria and algae can’t start to grow. It is recommended to run some water through them every 2 - 4 weeks. Anything longer than that, you have to add a special RO Guardian packet to each RO to ensure it stays in good shape.

PROS:

• Affordable to maintain

• Works in high TDS areas

• Can add a booster pump for greater flow

CONS:

• Expensive to get started

• Harder to maintain

In the Field...

Setting up both systems is pretty similar, hose to the inlet, hose to the outlet. However, with an RO/DI unit, you’ll find that there is waste water that is produced from the RO membrane(s). That waste water will flow the entire time you are using it so you have to find a suitable place for the discharge. Usually into the lawn or garden bed is fine. This waste water won’t hurt the vegetation. Almost all RO/DI units come on a frame with wheels so they can be wheeled around the jobsite. DI units sometimes have wheels, otherwise, straps or handles can be added to make them easier to carry. If you get to your client’s property and find that they have terrible pressure at the spigot, you can add a booster pump between your system and the source water to increase flow. With a DI unit, you can’t add a booster because you don’t want to push the water through the resin too fast. If you do, it won’t be able to filter correctly. 

Which is Better for a Beginner?

Some window cleaners like to think, “I’m just starting, I’ll just get the DI Tank for now.”, but depending on where you’re working, it could end up being a wasted investment. All of the XERO Purification Systems are designed for ease of use, so there isn’t much more to learn about the RO/DI units vs the DI systems other than understanding filter changes. If you start with a more affordable RO/DI unit and realize down the road that you need more flow, it’s always possible to add a booster pump to get more out of the system. However, if you start with a DI only system, you can’t later add an RO membrane to it, you’ll have to invest in a brand new unit.

Do Your Research

Now that you understand the strengths and weaknesses of both systems, it’s time to choose the one that’s right for you! If you’re having trouble making your choice or still not sure where to start, we can help. We are always ready to lend a hand and are available by text, call, email, or chat. Thanks to our many years of experience in the field, we can guide you in the right direction. Happy cleaning!

Meet the Author: SteveO is loved by his fans on YouTube where he demonstrates new tools and how to clean windows. He's continuing to share his wealth of knowledge for both aspiring and seasoned water fed window cleaning professionals.