Professor POU/POE – September 2012

Sept. 11, 2012

This month’s topics: Iron filters, silt and clay, GAC and resin, dead water.

Q: I was hoping you could point me in the right direction for selecting a filtration system for iron removal from my well water. After lots of online research I’m a little overwhelmed at the types of filtration systems for iron removal. Based on reviews I can’t tell what’s true or not. Do you have any recommendation as to what type of system I need based on the results below?

My water analysis is:

  • Chloride – 2.6 mg/L
  • Nitrate – 0.61 mg/L
  • Calcium – 0.45 mg/L
  • Copper – < 0.010 mg/L
  • Iron – 2.0 mg/L
  • Hardness – 2.6 mg/L
  • Magnesium – 0.35 mg/L
  • Manganese – 0.012 mg/L
  • Lead – < 0.0020 mg/L
  • Zinc – < 0.010 mg/L
  • Alkalinity – 67 mg/L
  • pH – 7.3.

A: If your hardness was greater I would recommend a water softener for both iron and hardness removal. If the iron was greater I would recommend an iron removal system that would require an oxidizer followed by filtration.

With the given water analysis I recommend a single tank iron filter containing Birm, a filter medium that will remove the 2.0 ppm (mg/L) of iron. At the iron level in your water this medium will remove it whether it is dissolved (clear, with no color), or already oxidized (colored).

I see no other problems with the rest of the water analysis.

Q: I currently have had a turbidity problem with my surface well. This well provided me with clear drinking water for many years until last month when I tried to dig a couple of feet deeper in order to get more water. I then found the water to be cloudy as if it contained clay.

Could you please tell me the best way to filter the cloudy water in order to remove the clay?

I thank you in advance.

— Jean – Montreal, Canada

A: You are dealing with very fine turbidity here. Speaking in general terms, clay and its close cousin silt are larger particles than bacteria and cysts. The distinction between silt and clay varies by who is defining it. Geologists and soil experts consider silt to be greater than four to five micrometers (microns or µm) and clay to be over two µm. Other sciences, like geologists, also use four to five µm and colloid chemists, one µm as a cut-off point.

I recommend either a large cartridge filter or multiple smaller ones plumbed in parallel that are rated to filter down to the micron size of two as a beginning. If these plug-up too quickly try a filter with a lower micron rating. If your turbidity is very concentrated then precede the cartridge filter(s) with a backwashing filter tank containing a multilayered filter bed. This will remove particles as small as about 15 microns.

Good luck.

Q: Thank you, David, for taking my questions. Our water professional here in Houston suggested I contact you. I have been researching water filtration systems for almost a year and find the information available very confusing and contradictory.

Here it goes:

  1. Is it necessary to have the carbon filter and water softeners in two separate tanks? I heard that one deteriorates the other.
  2. Is GAC good for the whole house? I heard it’s the only way to go because the solid block activated carbon (SBAC) is too restrictive for water flow for point-of-entry (POE).
  3. Is there any system that you recommend? We are targeting mainly chlorine with carbon and radium with a water softener. We will also add RO and ultraviolet in the kitchen for radium polishing and bacteria removal, respectively. We are also considering silver activated carbon. As far as the silver activated carbon cartridge is concerned, I have read several articles on trace amounts of silver found in the treated water with these systems, which is the reason I am reluctant about the silver.
  4. I forgot to mention that we are also concerned about removing fluoride, which I understand RO can do to a certain extent.
  5. What do you think about the NSF/WQA certifications?

I appreciate your time immensely. I don’t know where else to turn to get unbiased opinions.

Thank you so much.

— Houston, Texas

A: Although a combination of granular activated carbon (GAC) and softening resin are often layered in one tank, I do not recommend this. The concept of one deteriorating the other makes no sense to me. But, when backwashing the layered bed, the two media mix and the layering no longer exists. Carbon will normally be exhausted long before the water softening ion exchange resin at which time the carbon alone cannot be removed. New carbon can’t be added because the bed will then be too deep. At this stage the carbon is doing nothing for you, you can’t separate two, and you end up with a water treatment bed whose carbon component is no longer functioning. A solid block filter will cause much more pressure loss than the GAC filter tank.

Two separate beds, or tanks, are required. With the carbon placed first, it will remove the chlorine. Following this the softener will remove hardness, iron and radium.

The likelihood of needing the RO for radium removal is nil because the softener removes radium more efficiently than hardness.

RO is meant to reduce the total mineral content of the water (TDS). Usually this is not necessary unless the TDS is over 500-600 ppm. However, it is a good technology for removing silver and fluoride. Although it is unlikely that a small amount of fluoride or silver will pass through a RO membrane, neither one is harmful in low concentrations.

WQA and NSF both use the same testing standards for evaluation of water treatment equipment. I recommend that you look for treatment that has been tested by them for the particular contaminants that concern you.

A UV disinfection unit is needed when the water is known to contain bacteria or other pathogenic microbiological species. If you are concerned about microbiological growth in the treatment system, whether you have a RO storage tank or not, you can do so, but the bacteria found there will be common airborne bacteria that we experience continually. I suggest trading the RO and the UV for a silver activated carbon cartridge on the drinking water faucet.

Q: I’d like to hear from you about the claim that distilled water is dead water and does not have oxygen in it. I’ve received explanations for this. The most logical one is that if there’s no oxygen, it can’t be water. I’m sure you would confirm, but what else can you say to dispute it?

Thanks for your time and response.

— Judy – San Francisco, Calif.

A: Well, I’ve never heard of water called “dead.” It sounds like anti-distilled water sales talk.

Water, chemically, is H2O. The “O” stands for oxygen. Therefore, all water contains oxygen. Common water, from a surface source or a well, also contains up to about 20 “mineral” compounds, which are harmless and often necessary to our diet. There is nothing wrong with distilled water (no minerals) because we receive minerals in our food.

On the other hand, the distillation of water serves no purpose unless there is something proven to be harmful in it that distillation will remove.

David M. Bauman, CWS-VI, CI, CCO, is technical editor of Water Technology® and a water treatment consultant in Manitowoc, Wis. He received his B.A. from the University of Illinois in Industrial Design. He can be reached by email at: [email protected].

To pose a question to “Professor POU/POE,” go to, click “Ask the Professor” and follow the instructions.

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