The final (?) word on salty car wash water
Q: I just read your column “Is salty water reused in car washes?” As a retired chemical marketer who has dealt with salt solubility issues, I suggest you look further into the issue of whether there is appreciable salt in recycled car wash water. I fear that Mr. Wulf is misinformed if he believes that filtration removes most of the salt from recycled car wash water. Most road salts are either sodium chloride (rock salt) or sometimes a concentrated solution of calcium chloride in colder weather. Sodium chloride only precipitates (falls out of solution as a filterable solid) above about 23-26 percent. Below those concentrations salt cannot precipitate. And the warmer the water gets, the higher the soluble salt concentrations can get. While filtration can remove much of the solids (dirt and grit) from recycled wash water, it can only remove solids. So even recycled filtered water can still contain salt.
— S.B., Chicago A: Thanks to you, S.B. and several other readers who know their chemistry. About the only true way to remove the salt is through distillation or reverse osmosis. Nevertheless, rinsing the undercarriage with saline solution is better than allowing the buildup of salt to eat away at your Edsel.
We asked Eric Wulf, CEO of the International Carwash Association, for clarification.
“Most car washes have, essentially, three types of water: fresh (from the municipality), recycled (that has been filtered, either cyclonically or biologically) and reverse osmosis. Some can actually have a fourth — rainwater recapture. Reverse osmosis would be the most purified water, similar to many home filter systems. Reverse osmosis is used as the final rinse, to make sure that the car will dry without spots. It is usually not used for undercarriage washing.
“It will depend upon the car wash you visit, which of the above mix you are getting — but you are likely getting all three for the undercarriage wash. Some washes will feed the undercarriage with fresh water, so in that case the salinity would be low already.
“But even for those that don’t, they are using a mix of fresh, recycled and reverse osmosis (since that is recaptured by the recycling system), which means that the overall salinity of the undercarriage wash water will be better than the salt sticking to the car!
“No, filtration doesn’t remove all the salt but the processes that go into the mix of the wash water — filtration, reverse osmosis and fresh — means that salt is quite diluted.
“It’s also not uncommon for operators to add a rust inhibitor to the undercarriage water.”
Q: Having seen the question regarding “three on the tree,” it occurred to me that our federal government may want to mandate all vehicles to have manual transmissions. In this way, it would make it difficult for drivers to drive and text at the same time.
— N.K., Arlington Heights, Ill. A: Call your congressman. You may be onto something!
Rinsing the undercarriage with saline solution is better than allowing the buildup of salt to eat away at your Edsel.
Bob Weber is a writer and mechanic who became an ASE-certified Master Automobile Technician in 1976. He maintains this status by seeking certification every five years. Weber’s work appears in professional trade magazines and other consumer publications. His writing also appears in automotive trade publications, Consumer Guide and Consumers Digest. Send questions along with name and town to Motormouth, Rides, Chicago Tribune, 435 N. Michigan Ave., Fourth Floor, Chicago, IL 60611 or motormouth. tribune@gmail.com.