Homegrown solution to hard water spots

Q: What can I use to remove hard water spots from a double-pane window? The water spots came from the garden sprinkler. — Virginia B., via e-mail

A: “Hard” water is generally called such because of the amount of mineral deposits, especially calcium, it contains. It’s common throughout the United States, as groundwater often runs through sections of the earth containing limestone, chalk or similar minerals. Magnesium, iron and other minerals are also typically present in hard water.

Well water — from which some sprinkler systems draw their water — can contain much higher levels of minerals than municipal water, which has reduced mineral content due to the treatment process. Because the most common issue with hard water is the buildup of mineral scale on surfaces over time, homeowners using well-water-fed sprinkler systems should check the sprinkler heads throughout the watering season to keep scale from clogging the nozzles.

Which leads us, sort of, back to hard water spots on windows. These also can occur with nagging frequency and are difficult to clean off; mineral salts adhere to the glass quite easily. And depending on the mineral, store-bought window cleaners may not have any effect and can be counterproductive.

A homegrown solution that may work is to apply a thin coat of oil (lemon oil or even vegetable or olive oil) to the glass and let it sit for about an hour. The oil can soften the mineral scale and help lift it away from the glass. Then, make a thick paste of water and cornstarch (or baking soda) and dab on with a soft cloth or toothbrush, cleaning one section at a time in a circular motion.

Clean the entire windowpane with warm water and mild dish soap and check for remaining water spots; spot-clean with the paste and toothbrush and rinse. Once all the spots are gone, use an ammonia-based window cleaner to finish.

HOME TIP: Using commercial window cleaners on hard water spots can be counterproductive. Look for nonabrasive products specializing in removing mineral buildup from glass and tile.