How can chemistry help me clean hard water stains?

A basic knowledge of chemistry can make cleaning a snap. For example, you know those "hard water" stains in your bathroom? No? Oh, it looks like this . . . see the picture at right. They call it "hard water" because the water supply has a significant concentration of minerals such as calcium and magnesium. The nasty process starts when you leave the shower. The bathroom hardware is wet with water droplets adhering to the metallic surfaces. The thing is, the water droplets evaporate, but the minerals don't. The minerals actually crystallize onto your tub spout and handles, leaving behind a water-drop shaped  stain. Compounding the problem is the fact that soap also leaves behind a film. 

As an interesting side note, this means that if we could take showers in pure water, there wouldn't be spots right? Yes, that's why window washers use purified water to clean windows that are hard to reach with a squeegee. Once they scrub off all the dirt, the water will evaporate, and since there are no minerals in the water, it evaporates without spots! 

So, what is a human to do when it's their turn to clean the bathroom? The untrained bathroom cleaner, will pick up a bathroom cleanser and rely on muscle power and time. While this will get the job done, it exhausts two precious resources of a lazy person . . . time and effort. Another unfortunate consequence, is that many cleansers have some type of grit in them which works like sandpaper to remove the finish from the hardware. Eventually, the bathroom hardware will have to be replaced because it will look like it is prematurely 30 years old. 

The chemistry-wise chore doer uses those same resources, time and effort, to his advantage. The only difference is that chemicals are using time, and doing the majority of the work. See, the hard water stains are weakly basic like soap. Since most cleansers are similar, they are not very effective on hard water stains. One common pattern of chemicals reactions, is that acids and bases readily react with each other. So, what is a good acid to use on the water spots? Hydrocholic is too strong for typical cleaning, and will probably dissolve your skin away. But acetic acid (known to the populous as vinegar) is a weak acid which will react with hard water stains to create chemicals which will wash right down the drain. Here's what you do:

1. Buy a cheap spray bottle at the grocery store. 

2. Fill it with vinegar from your kitchen - do not dilute it.

3. Use the bottle to spray and soak the offending hard water stains. If you hate the smell of vinegar like I do, turn on your bathroom fan. 

4. Come back in 5 minutes. This allows the vinegar to soak into the deposits, and neutralize them. This is where you get to save the time and effort! If you care about the chemistry, here is a simplified example of the reaction . . .

CaCO3 + 2 HC₂H₃O₂ --> Ca(C₂H₃O₂)₂ + H2CO₃

5. Now, get your scrubbing implement, and wipe the stains away. It may take a little elbow grease, but not nearly like it would have without the vinegar. If there is a significant buildup, you may need another treatment. Here is an specific area that I scrubbed with a q-tip soaked with vinegar (compare to above):

An alternate that costs some money, is to employ a water softener. A water softener exchanges minerals in tap water with sodium, which is very soluble, and doesn't accumulate to the degree that calcium and magnesium do.

So, what do you really gain from this approach? 5 minutes saved where you weren't scrubbing, you've saved the frustration of the effort, saved the finish on your hardware, and felt the satisfaction of wielding your chemistry know how to work for you!