Background
Clay is one of the most common materials in the crust of the earth. It is the result of millions of years of break down and weathering of the rocks that make up this planet. It is composed of a fine grained deposit of minerals. Clay is able to hold water, is virtually impermeable when wet and cracks when it dries out. Clay particles range in size from 4 microns to .005 microns in diameter, which is far smaller than the human eye can detect. (1 micron is 1/100,000 of a meter.)

When mixed with water, clay particles form a colloidal suspension, i.e., the particles separate from each other and become suspended between the water molecules. Because their size is so small, gravity cannot overcome the forces that suspend them in water, so they stay in the water instead of settling out. Usually, the clay suspension cannot be seen.

If soluble iron or manganese is in the water, it can stick to the clay. When this happens, the iron or manganese is dragged through a water softener and shows up when oxidized, leaving the characteristic rust, beige or black staining associated with those metals. Clay can also remain on a person’s skin, causing the skin to feel very dry, almost like a film on the skin.

Symptoms
It appears to the customer that their water softener is not working even though the water tests as “soft”. The skin feels dry. The water may have a yellow or pale yellow color to it, which does not precipitate or settle out. A pale colored powdery dust may eventually appear in the toilet bowl. The house shows signs of iron or manganese even though their water treatment system checks out mechanically. The shower curtain may have a build up characteristic of hard water, though stickier. A house that has not had yellow water before, now has it after an air stripper / aeration system was installed.

Treatment
Sometimes a fine cartridge filter, (such as 1 micron or .45 micron) is able to trap enough of the clay to alleviate the symptoms. Some clays will pass right through even a fine filter, so the next step is to try flocculating the clay by chlorinating the water. The clay will sometimes then oxidize and become larger particles, or will stick to iron present and then be filterable. The normal process is to perform some modeling in the home to determine the most economically feasible treatment method.