Q: After living in the city all our lives, we recently moved to the country, where we immediately encountered deep well water. A white, flaky sediment that’s aesthetically unappealing — to say the least — settles out of this water in our drinking glasses. What is this substance? Is it harmful, and can it be eliminated without installing a water purifier?
Without knowing the specifics of your situation — such as the depth of your well, whether you use a holding tank and the geology of your area — I can make only a reasonable guess as to the composition of the “white, flaky sediment” that settles in your tumblers. My hunch is that the culprit is calcium carbonate, CaCO3, which probably dissolved naturally from limestone rock. At the temperature and pressure of the water deep in the ground, the compound is kept in solution, but at the temperature and pressure at the earth’s surface, the liquid becomes supersaturated, causing the CaCO3
If the substance truly is CaCO3, you probably need not try to remove it, except for aesthetic reasons. I’m not aware of any adverse health effects caused by ingesting the compound, especially in the amount you’re suggesting. Ion-exchange equipment will remove the material, but at significant expense and with the disadvantage of adding sodium to your water. Depending on the nature of your plumbing and your holding tank, you may be able to install a replaceable “rope wound” filter cartridge in the line that feeds into the sink, thereby trapping the substance before it flows from the tap. However, if the precipitation takes place in the glass itself, no amount of physical filtering will solve the problem. Other possible solutions, such as home-size distillation units or “reverse osmosis” systems, are so costly or difficult to run that you’d need tremendous dedication to use them to remove the flakes.David Burmaster is a consultant on surface and groundwater quality and hazardous-waste management.