De-ionization 101

De-ionization 101
Posted in: Reverse Osmosis
Deionization, commonly called DI, is complete demineralization of a water supply.  Specifically, the term deionization is used with respect to the removal of the cations and anions from the water.  In some cases, the water is passed through two separate columns of cation and anion resin.  These days, most deionization is accomplished with the use of mixed-bed DI resin. DI water is similar to distilled water, and while it produces water that is pure in a ionic respect, it does not remove bacteria.  Deionized water is commonly used in the following applications:
  • Medical
  • Laboratory
  • Pharmaceutical
  • Cosmetics
  • Electronics
  • Manufacturing
  • Reefkeeping
  • Humidification
  • Food Processing
  • Plating
  • Car Wash Rinsing
  • Industrial Processes
Typically, we see Mixed-Bed DI resin in tanks or cartridges (pictured above).  Year ago, many two column DI systems existed and even regenerate-in-place systems were common, but with EPA regulations the caustic and acidic nature of the regenerants have all but eliminated two column automatic regenerating systems.   Some critical water processes require DI water of varying grades of purity.  There are basically three (3) types of DI or ultrapure water.  Type 1 is used for semiconductor final cleaning, medical devices and water for infusion.  Type 2 is used in may labs, cleaning and food grade products and Type 3 is used for parts cleaning and general lab cleaning.  The table is listed below:         Here's the rub:  You can use high purity DI resin to deionize water, but the cost is typically 30 to 50 cents a gallon.   However, if you utilize reverse osmosis ahead of any DI system, the cost will typically drop to 1 to 3 cents a gallon.  If DI is your primary demineralization method the cost per gallon can be as high as 50 cents a gallon, but if DI is the secondary deionization (or polishing) method and reverse osmosis is the primary demineralization method, the cost drops to as little as a penny a gallon.  Yet, there are still people who use DI as the primary demineralization method and they are deeply loved by the companies who deliver DI tanks. I recently installed a RO system followed by DI polishing at a factory who was spending over $70,000.00 a year on DI tanks.  The entire system cost $31,000.00 and the yearly DI cost is now less than $5,000.00.  The water quality is the same.  They don't have to wait on deliveries and the cost is dramatically lower.  Why would anyone do it the DI only method?  Answer: They either have too much money and don't care or they just don't know any better.  Now they do! While there are many types of DI resins, we primarily deal with three:
  • Standard Mixed Bed DI Resin - Typically is for water up to 16 megaohms;
  • Semiconductor Grade Mixed Bed Di Resin - Can deliver up to 18.2 megaohms; and
  • Color Indicating Resin - Turns from blue to brown when it is exhausted and generally does not deliver much more than 10 megaohms.
The Semiconductor grade mixed bed DI resin is the most popular because it delivers the highest quality water and has the highest capacity.  The color indicating resin is popular in reefkeeping, but it is more expensive and delivers lower quality water.  Some people just like to use it because with a clear filter housing, they can observe when it is exhausted.  It's actually less expensive in the long run, to use the standard semiconductor-grade resin, and buy a conductivity monitor. In conclusion, with proper pre-treatment, a DI system can consist of a cartridge or cartridges that can be easily changed at infrequent intervals instead of relying on delivery of a large, heavy DI tank.
August 30, 2012
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Taylor Overeem
April 21, 2017 at 7:37 PM
Id love to go away with di but i have a mobile auto detailing business and cant use ro due to renting a condo with no water access
Kevin Livingston
July 12, 2017 at 11:21 AM
How do you measure D I Water conductivity? Thank you for your response of last evening. Kevin Livingston
Joe Elliott
July 29, 2019 at 1:46 PM
What about the excessive waste water that comes with RO's. Can anything be done with that?
Mark Timmons
July 29, 2019 at 3:18 PM
The newer high-efficiency commercial RO systems waste 1 gallon for every 4 made which is not much. That waste can be reused for any number of uses such as flushing toilets, irrigation and the like. But, sometimes we focus on the wrong thing. Do you know how many gallons are wasted in manufacturing a pair of jeans? 1,700 gallons. How many pair of jeans do you own? It takes hundreds of gallons of water to make a cubic foot of DI resin. If you can increase it's life 10, 20 or 50 fold, you are also saving water.
January 22, 2020 at 5:33 PM
Mark, Crazy question here, but I’m friendly with a fellow who owns a business that processes and delivers DI water to smaller users in a four state area. He’s looking to sell his business at what I think is a reasonable cost. I haven’t looked into it much but it seems like a pretty safe business to get into. Again, I’m just starting to consider this as I’m ready for a new career. Financials aside, are there any negatives to entering the DI processing and delivery business. I know how general that question is, but his customer base seems pretty solid.
January 22, 2020 at 5:41 PM
Sorry I know that was a weird question, but I’m just looking for some input. I’ve run my own specialty contracting business for 25 years and I’m thinking about moving on. I’m sure that getting involved in someone else’s business has a lot of ins and outs to it, I’m more looking for your overall view of the industry and and positives or negatives. If you don’t want to answer here, feel free to email me directly. I appreciate it.
Mark Timmons
January 24, 2020 at 3:36 PM
It's not a strange question. I do not think it is a safe business, however. As consumers become wise to DI, they will soon find out they can make their own for a lot less than anyone can afford to deliver it. It will go the way of milk delivery. It is very inexpensive to buy a simple system that makes DI water and consumers are not stupid. His customers are the people we want to talk to. You asked. I responded! ;)
Stephen Dowd
April 28, 2020 at 1:08 PM
We're looking at using a DI system to wash down an aircraft after washing. Our plan is to use a 500 Gallon tank on a trailer and take the cleaned water to the point of use. Do you have a RO system that we could use to accomplish the same task.
Mark Timmons
April 29, 2020 at 12:55 PM
Most likely a RO system would deliver the quality you need, or it could serve as pre-treatment for the DI cutting your costs by 10 Times. I have included Mike Beck, our DI expert. He will help you out with the best solution.
June 15, 2020 at 8:54 PM
Hello, looking for a cost effective system to provide me enough water to rinse my car after washing. I have a well with water at 450 tds. Currently looking at DI tank from local vendor that should get me around 500 gallons for $250. From what I’ve read RO can be cheaper but seems to have higher up front cost and requires pressurized storage tank and may still require DI after. Can you recommend a system that has low up front costs as low as DI. Seems to be a good sized market for such a system for auto detainers and folks who wash at home but no one has packaged an RO unit to compete with home DI systems like CR spotless and DI rinse.
Mark Timmons
June 15, 2020 at 10:32 PM
This is a very good question and I will make it a Blog later this week. Stay tuned!