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Pure Water Frequently Asked Questions

We often get asked questions about pure water, DI tanks, reverse osmosis, membranes, resin and just about anything relating to pure water window cleaning.  So we thought it might help some of you if we answered the seven most common questions we get asked.

Top 7 Pure Water Questions

1. Pure water – tasteless, colourless and odourless, is often called the universal solvent. Which minerals or salts being present in water , i.e. calcium, magnesium, potassium, sodium, bicarbonates, chlorides and sulfates can harm windows?

A) Yes, in theory “pure water” is tasteless, colourless and odourless. However, DI water actually has somewhat of a “fishy” smell. Without getting too technical, I’ll just say this is a result of the chemicals used to regenerate the resins. All minerals or salts can leave spots on windows. They may not “harm” windows but they will, in most cases, leave spots at low levels.

2. Would a deionised water window cleaning set up get more gallons of water if they were to run 2 tanks? (One filled with premium anion resin, and another tank filled with premium cation resin) Or would a mixed bed set up be a better solution for a window cleaner?

A) Yes, a two tank set will definitely have more gallons capacity than a single tank of the same size. There is simply double the amount of resin. Therefore, a two tank set will get at least double the capacity of a single tank. Again, without getting too technical, I will also say a two tank set up may get as much as 3.7 times the capacity of a single tank depending on the type of resin used. ex. A 9″X44 set of weak base de-ionisers offers 42,000 grains of capacity while a 9″X44 mixed bed only offers 11,300 grains.

3. Most window cleaners utilise the customers water spigot as their water source, what are the effects of chlorine on pure water from this type of scenario?

A) In the window washing scenario, chlorine in the raw water doesn’t necessarily have an adverse effect on the windows. However, chlorine will over time negatively impact resin causing it to break down and lose capacity. Anytime chlorinated water is fed into a deioniser, it should be run through a carbon filter first.

4. What are the direct effects of high TDS levels on a DI tank?

A) High TDS will simply exhaust the DI tanks faster. ex. a 9″ X 44″ weak base set of deionisers has approximately 42,000 grains of capacity. Therefore, water at approximately 171 TDS or 10 GPG (171 divided by 17.1) will allow approximately 4,200 gallons between regenerations OR water at 340 TDS will allow about 2,100 gallons. (342 mg/l TDS divided by 17.1 = 20 GPG divided into 42,000 grains of capacity.

As I said previously, chlorine will degrade the de-ioniser resin and cause it to break down, thereby reducing and eventually eliminating its capacity

5. Is anion resin subject to organic fouling from non cationised water?

A) Yes, anion resin may be subject to organic fouling whether there is a cation tank in front of it or not. This is not typically a concern in the window washing scenario. It would be more of a concern in higher purity or more critical applications such as micro electronics or medical applications.

6. Will hot water itself ruin a DI membrane?

A) Hot water is not good for deioniser resins. Most resins can only handle up to 120 degrees F before they start breaking down. There are some more expensive resins available that allow up to 160 degrees F.

7. How does DI take the minerals out of water? What is the chemical process on a molecular level?

A) I believe I already provided some information about the Fundamentals of Deionisation by Ion Exchange. I will do my best to give it to you in a nut shell. Water generally contains dissolved mineral salts that are separated into positive and negatively charged ions. Positively charged ions (cations) are exchanged with hydrogen (H+) in cation resin and negatively charged ions (anions) are exchanged for hydroxide ions (OH) thus, the process forms water (HOH) or (H20).

These are the “simple” answers. If you want more detail, I recommend the Water Quality Association website, www.wqa.org.