Residue from the Dishwasher –VAMWON Notes from the Field

VAMWON Notes from the Field are a series of stories of the questions and sometimes the solutions I’ve encountered as a volunteer with VAMWON. The Virginia Master Well Owner Network (VAMWON) is an organization of trained volunteers and extension agents dedicated to promoting the proper construction, maintenance, and management of private water systems (wells, springs, and cisterns) in Virginia. The Cooperative Extension Services in Virginia manages the program and have numerous publications and fact sheets that can help homeowners make educated decisions about their drinking water. The VAMWON volunteer or Agent can help you identify problems with the water system and provide information on suggested treatments options and other solutions. You can find your VAMWON volunteer neighbor through this link by entering your county in the search box.

Below is an email I received (my contact information is available through the VAMWON web site).
“I have another mystery, if you are agreeable to finding another solution. For several years, I have noticed that when I drink water out of my glassware, the water smelled "dusty"....which I assumed was the residue from the dishwasher detergent. I would try at different times to solve this problem by rinsing an extra cycle, or minimizing the amount of detergent. I am down to two tablespoons now. The dishes still get clean, but the smell persists.
(1) I assume this is not a dangerous occurrence.
(2) Is there another test that we should have included in our sample that we will take this week ...? “

The homeowner had just forwarded to me the analysis results from their most recent water testing. The homeowners have three grandchildren under the age of 3 year’s old living in their home so they have been testing their water regularly using the WaterCheck package available from National Testing Laboratories, Ltd. If your home drinking water is supplied from a private well, you are responsible for ensuring that your water is safe to drink. There are no requirements to sample and sample analysis can be quite expensive depending on what analyses are performed. The homeowner is responsible for paying for the sampling.

In the past the homeowner had told me that they had high iron and hard water and a treatment system, but the test results showed low iron and manganese and water that were not particularly hard. I questioned where the sample was taken and the homeowner assured me that they took the water sample from the back outside water spigot (after properly cleaning it) that is after the simple sediment filter but before the water softener. The water treatment company they consulted had reportedly tested their water and found high iron when they sold them the water treatment system that apparently consisted of a whole house fiber filter and a water softening system.
I was a little puzzled by the results and I had asked the homeowner to check their toilet tanks for a red or rust colored slime. They found no slime in any of the toilets, but did find a small amount of sediment in the bottom of each toilet that is a rusty red color and clouds up the water when swirled with a toilet brush. They also found a bit of milky colored substances around the black gasket that the flapper on multiple toilets. When she scratched off a bit with her fingernail, it floated up like tiny pieces of “corn starch.

What she described sounded like a precipitate (calcium carbonate, sodium chloride) its white color would indicate few impurities, minerals and impurities tend to add color to precipitates. Though it is possible that the water treatment company performed a coagulation test, but most people are honest though their test are often very limited in scope. Considering the problem assuming the water treatment company actually found iron before they sold the homeowner a treatment system and now the water tests were non-detect for iron I realized there could be a simple explanation given where the sample was taken. Particulate or colloidal (Ferric iron (Fe3+)) may be the form of iron present in the water supply. This form of iron appears as particulates in the oxidized form. Particles in suspension in the tap water result in water that has rust, red or yellow color when the particles settle.

One of the recommended treatments for iron is aeration followed by filtration – This method is effective for treating iron and manganese with a combined concentration of between 5 and 10 ppm. Air is mixed with passing water to oxidize the iron and/or manganese producing particles that can then be filtered out of the water by a fiber filter. When water leaves the well it is exposed to air that can have this effect depending on the flow rate and holding times in the system. The water then passes through a filter to screen out particles of iron and/or manganese. An oxidizing filter treatment system is the next level of filtration. It is effective in treating iron and manganese at combined concentrations of up to 15 mg/L. Because oxidizing filter units combine oxidation and filtration, they can be used to treat water with dissolved and/or particulate iron and manganese.

It appeared that the filter on the homeowners system was doing a decent job of removing the iron oxide particles. The more oxygen the water is exposed to before the filter, the better it works. So when the pump is working full out, there is less time for oxygenation in your pressure tank and your filter will be less effective. Retesting the water supply ahead of the filter could confirm this, but would be an additional cost. The effectiveness of the installed water softening system for iron removal is very limited. Iron and manganese present in combined concentrations of 5 ppm or less can usually be removed by using an ion exchange water softener. However, this is not an optimal removal method.

As for hard water, some University extension offices designate 125 ppm as the cut off for hard water others use 100 ppm. No matter which standard you use 120 ppm the level present in their water is only marginally hard. My own water is significantly harder and I do not treat. I just use detergent based soaps and lots of vinegar to treat the limescale. I just assume my hot water heater will be a short lifer. In addition, the water softening system might impact the life of your septic system. The salt reportedly reduces the life of the septic tank (www.watersystemscouncil.org ) and may impact the peat medium and soil in the drainage area. Also, softening can make your water slightly acidic and in that way reduce the life of all your fixtures. So softening becomes a trade off and is best only used if you prefer a slightly salty water residue. I believed that the residue on the dishes might be simply salt and suggested they try turning off their softener.

The homeowner chose to turn off their iron exchange water and found that the “dusty smell” and residue on the glasses disappeared. In addition, she claims to be much happier with the “feel” of the hard water.