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Which spotless water system is right for you?

People are always asking us to compare our products with other de-ionizing systems on the market in terms of production, features, and price. We know that it can be confusing because some companies claim to have a spot-free product that is really just a water softener. Others make claims that they can get 50 gallons of de-ionized water from a system that you can hold in one hand, and you ask why ours “gets so little” in comparison when it is a much bigger system. Here, you will find all the information you need to ask the right questions and decide which system is right for you.

Total Dissolved Solids

First, let’s talk about spot-free water. Based on our tests, we consider “spot-free water” to be water that contains less than 20 parts per million (ppm) of Total Dissolved Solids (TDS). TDS are made up of all the Calcium, Magnesium, Potassium, Sodium, etc. that are typically found in your water unless some or all of them are removed by reverse osmosis, distillation, or de-ionization. So-called “water spots” are actually caused by the minerals that are left behind when “dirty” water evaporates; de-ionization removes all of these minerals so there is nothing left to spot when pure water evaporates.

How much “spot-free” water can a system produce?

For the most part, the answer can be derived from a mathematical formula that is based on two things: the TDS of your water and the volume of virgin resin in the system. The technology of de-ionization has been around for a long time, and it is a mature technology. There is no magic or revolutionary technology out there that will give you more gallons of “spot-free water” with less resin. Once you know the answers to the following two questions, you can calculate the approximate yield of spot-free water.

What is the TDS Level of your tap water?

Your system comes with a TDS meter that will give you that answer, but you can also buy a simple TDS meter at any pool equipment store, home improvement store, or even on ebay. Keep in mind that the TDS level can fluctuate from your water source on a minute by minute basis, but it usually stays within a certain range. You can even try calling your local water district and asking them what the average TDS level is for the water coming to your house. The TDS level can also vary significantly from one city to the next, from one state to the next, and around the world.

For example, here in San Diego, we have some of the “worst” water in the country with an average TDS around 400 ppm (parts per million). (You definitely don’t want to wash your car without DI water in this city…which is exactly why we invented the CR Spotless Water System back in 2003.) Another city in Orange County, CA states on its website that their TDS level is only 40 ppm which is the same as the water we tested in Portland, OR. In Grand Rapids, Michigan, the water tests at 170 ppm. A customer from eastern Kentucky told us that their water tested at 80 ppm.

We use a national average of 250 ppm to “conservatively” state the number of gallons of de-ionized water that our systems will produce on “average.” Be careful and make sure you ask what TDS level other companies are using to compute the number of gallons of de-ionized water that their systems will produce. Most use a TDS level of 100 ppm which will make their systems appear to produce twice as many gallons as ours, but not so in reality. It’s best to just calculate the number of gallons you will get from each system that you are investigating based on your TDS level. That way you’ll know.

What is the quantity of de-ionizing resin used by the system?

This number is usually expressed as a fraction of a cubic foot. For example, our 10” models hold .085 of a cubic foot in each of the two cartridges so a total of 1/6 or .17 of a cubic ft altogether. Our 20” systems hold twice that or 1/3 (.33) of a cubic foot in two 20” cartridges. Again, it can be calculated if you know the diameter and the usable height of the cartridge. But the supplier in question should be able to answer this question just like we have done for our systems above.

The Magic Formula

So here it is…the magic formula that will reveal how many gallons of spot-free water that you should be able to get out of a de-ionizing water system: 235,000 / TDS X Volume of resin = Gallons of “Spot-free Water”. Refer to the chart below. For comparison, we have used the volume of resin contained in one of our competitor’s small hand-held systems (.02 cu ft) to the resin that can be found in our 10” (.17 cu ft) and 20” (.33 cu ft) systems.


Vol of Resin
(cu ft)
# Gals from
.02 cf
Vol of Resin
(cu ft)
#Gals from
.17 cf
Vol of Resin
(cu ft)
# Gals from
.33 cf
50 ppm .02 (1/38) 94 .17 (1/6 ) 799 .33 (1/3) 1551
100 ppm .02 (1/38) 47 .17 (1/6 ) 400 .33 (1/3) 776
200 ppm .02 (1/38) 24 .17 (1/6 ) 200 33 (1/3) 388
400 ppm .02 (1/38) 12 .17 (1/6 ) 100 .33 (1/3) 194
Flow Rate: .2 gpm 2 gpm 2 gpm


Other Factors:

There are other factors that will influence the actual number of gallons of spot-free water that a system will produce. For example, flow rate is very important in determining whether or not the water will be spot-free. If the water flows through a system too fast, it may not be “purified” enough to prevent spots.

How fast can the system produce De-Ionized water?

Just how quickly a system can produce DI water ((gallons per minute (gpm) = flow rate)) is also a mathematical equation. You need dwell time on the resin in order for the minerals (TDS) to be removed and exchanged with Hydrogen and Hydroxide; it is not instantaneous. Flow rate again is based on TDS level and Volume of Resin. The more resin you have in the system the faster you can flow the water through it and vise versa. Also, the more TDS you have in the water, the longer it will take to de-ionize it and again vise versa. See the recommended Flow Rates on the chart above for each of the 3 system sizes above.

At these recommended flow rates, the output TDS level will be 0 ppm until the resin nears depletion. You can flow water faster through these systems but you will not get what we consider “Spot-free Water” (less than 20 ppm TDS). The water will obviously be cleaner than regular tap water but it will not be spot-free. For instance, flowing 400 ppm TDS water through our DIC-20 unit at 6 gallons per minute with brand new resin will yield water with a TDS level of 85 ppm…cleaner, but not “spot-free”.

That is why some of the smaller systems in the market seem like they work in the beginning, but you’d have to restrict the water flow to nearly a trickle (.2 gpm) to keep them producing spot-free water given the small volume of resin that is in them. Most of our customers want to have a flow rate that produces enough water and pressure to be able to wash a vehicle or house windows with ease.

CR Spotless Water System - TDS Meter

Integrated Battery Operated TDS Meter 

To be absolutely certain that you are using spot-free water, you need to have a TDS (total dissolved solids) meter that constantly measures the TDS level of the water coming out of the system. That’s why all of our systems include an integrated battery operated TDS meter; to give you the peace of mind that the sun won’t weld spots into your work surface!

Use our system with confidence

With a CR Spotless Water System®, you can be certain that we have designed, tested, and built de-ionizing systems that will provide you with many years of spot-free rinsing of your cars, RVs, motorcycles, house windows, solar panels and more.

Please Contact Us with any questions.