Professor POU/POE – November 2012

Nov. 7, 2012

Q: We are using a 10-inch calcite cartridge filter to raise the pH of reverse osmosis water as it comes out of the membrane before …

Q: We are using a 10-inch calcite cartridge filter to raise the pH of reverse osmosis water as it comes out of the membrane before going to the storage tank. The water then goes through a 10-inch carbon cartridge before it goes to the faucet. This is our typical residential system.

There have been many requests from our customers who are worried about the RO water being acidic. The pH is lowered maybe one point during the RO process and we are raising the pH to 8 to 8.5 using the calcite filter. Are we doing this the correct way? The use of 20 percent Corrosex with calcite raises the pH higher, but I also think we get a bitter taste complaint on occasion. The debate on alkaline water seems to have people on both sides with a varied opinion. Thank you for any input you may have.

— Arizona

A: If the corrected pH is 8.0 to 8.5 and you have raised it about one then the original pH, after RO, was about 7.0 to 7.5. If this is correct I would say the water does not need pH correction. A pH of 6.5 to 8.5 (EPA Secondary Drinking Water Regulations) should be very acceptable to the taste and the plumbing system.

If, on the other hand, the RO water is below 6.5 then the calcite cartridge is a good solution. Do not use Corrosex for the reasons that you have stated.

As for the debate on alkaline water (and I’m assuming you refer to health benefits), I know of no benefit to it. I and others have written about this before.

Q: I have a potable rainwater system here at my house (

The 2,000 square feet of zinc/aluminum coated standing-seam roof collects rain and sends it to two 3,000-gallon concrete cisterns.

A Grundfos pump withdraws the water, pumping it through a 5 micron particle filter and a 15 gpm UV.

A large hickory tree overhangs a portion of the roof. Every spring, the hickory tree (a member of the walnut family) exudes a substance that acts as a herbicide and contains a fair load of tannin. Using the collected rainwater to hydrate houseplants has actually killed several of them — their leaves turn black.

The rainwater has a nasty odor and taste, and when it’s heated (for domestic hot water uses like showers) the odor is exacerbated.

We tested the effectiveness of activated carbon by using pitcher water filters. The carbon seems to remove most of the color and taste/odor. So, I’ve placed a GAC radial-flow cartridge downstream from the UV. I’m dealing with leaking plumbing unions now so it’s not fully functioning yet.

After three years of pursuing a solution to this problem (besides a chainsaw, of course), is the first website I’ve found that directly addresses the tannin issue. And, it’s the first place I’ve heard about anionic resins for extracting tannin. My question: From what I’ve read, including on your site, it appears that the low pH (5.5) of the rainwater will limit the carbon’s ability to capture the tannins.

Do you have any comments, thoughts or advice about our situation?

— Oregon

A: Walnut trees are notorious for exuding a toxin called juglone. Hickory trees do the same thing only to a lesser degree. Almost any tree overhanging a roof will impart tannins to rainwater. The juglone, from leaves and roots, is a toxin to other plants nearby and the rainwater-containing juglone as you have found is a toxin when used for watering. Juglone is also harmful to pets and livestock and to some degree acts more like an allergen to humans. I found some evidence that juglone may be considered a tannin, also.

Activated carbon is not commonly used for tannin removal. Certain anion-exchange resins are particularly good for tannin removal. These function similar to a water softener. Since sodium chloride is used as a regenerant, I suspect you don’t want to do this in a “green” house, but it would probably work. If you pursue this, work closely with a resin manufacturer.

Otherwise, I’m afraid you may have to go the chainsaw route. In this situation I wouldn’t want any trees to overhang the house.

Q: Recently my house was struck by lightning. It traveled through copper water lines and jumped to the electrical wiring for my water system. The next day I noticed my water was a weak iced tea color. My service technician came out and replaced the tannin resin, which was fouled and water clarity since has returned to pre-lightning quality.

From what I’ve been able to research (I’m no electrochemist), I believe the electrolysis of the brine and iron in the water softener may have affected the charge and therefore, capacity of the anionic resin with the lightning as the source of current.

Or, is it possible the lightning grounded through the well and changed the water source (since new tannin resin and citric acid in the brine tank seemed to resolve the issue). Could the electrical charge from the lightning have caused the tannin resin to foul?

— Florida

A: I would strongly suggest that you make every possible effort to find a one-quart sample of the old resin and have it analyzed by a resin manufacturer. My talks with one manufacturer revealed that they haven’t heard of this, but it also has never been studied.

Fouling would not result from the lightning, but physical damage could readily be determined. Hardness and iron should not come in contact with the anion (tannin) resin. Water softener resin (cationic) would suffer the same damage if it were exposed to the same conditions.

Although it’s possible that lightning damaged the resin, it would only be speculation to try to explain it.

Q: I enjoy reading your articles in Water Technology and hope you can help me. I am a state licensed master plumber and also know a little bit about water softeners and iron filters as I live in a rural area where most homes have their own well. Today I was on a service call and there was a pinhole leak in the 3/8-inch type L soft copper cold water supply tube to the kitchen sink. Since both tubes were copper and about 30 inches long, I suggested to the homeowner that we change both. It’s been my experience that if you have one pinhole leak, others will eventually follow.

I remembered reading something about green staining on fixtures being caused by acidic water so I tested the pH. Imagine my surprise when it was actually alkaline — 10.7. I tested twice to be sure. Now I’m at a loss as to what to do to correct the problem. I called my tech support from my filter supplier and was told how to lower it closer to 7.0, but he also said that he did not believe the alkalinity would cause the pinhole leak.

— Florida

A: You are correct that pinholes are often the result of acidic water. However, acidic water most often creates a more uniform interior surface deteriorization.

The normal progression in copper pipe is that after a few months in service a copper oxide coating forms on the pipe interior. This typically acts as a protective layer against further corrosion. Acidic water would prevent this formation or hardness could deposit on it.

The high alkalinity (pH) is highly uncommon and should be retested with a different test kit. I also recommend a complete water analysis, especially alkalinity, TDS, hardness and iron.

For the reader, the plumber and I have had a few email communications between his first question and my answer. We have established the following.

The cold side actually broke quite easily where the pinhole was and both the hot and cold tubes were coated with a blue/green buildup inside throughout the entire length of the tubes … not very thick. Also, there was a blue/green stain on the exterior of the pipe, but not where it was leaking. No soldering or flux was used in this area. All adjacent connections utilized compression fittings.

The dealer wondered if there might have been a small kink in the pipe at the leaking point but no longer can tell. A kink in the pipe could eventually erode due to increased flow velocity at that point. There were no bends or elbows at the leaking point. The house was built in 1995.

At this point I believe a more thorough water analysis is required and that this problem is likely to exist elsewhere in the house.

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