Car washing and water spots

A while back I wrote a piece about water spots, what causes them, and how they can be avoided. Here is the link: http://priuschat.com/forums/knowledge-base-articles-discussion/18275-what-causes-water-spots.html

I recently received a request for more information relating to deionized water. I will post it here in case it is of interest to any others. The following is a quick, non-technical look at deionized water:

What is deionized water? To understand that, we need to first understand ions. Many chemicals are composed of two elements holding hands through an ionic bond. One has a positive charge, the other negative. They stick together like two magnets. Ordinary table salt is a good example, composed of sodium and chlorine. When dissolved in water, the sodium and chlorine split apart and float about as ions. Sodium ions have a positive (+) charge, while the chlorine ions are negatively (-) charged. When the water is evaporated, these two ions go back together and we are left with a small pile of salt.

Hard water contains calcium salts, dissolved in the same fashion as the table salt in our example. When you wash a car with hard water, the calcium ions do two detrimental things: 1) The calcium reacts with soap and neutralizes some of the soap's cleaning action, and 2) The calcium salts are left on the surface after the rinse water dries, leaving water spots.

The neutralizing action of hard water is not a big problem. It can be overcome by using more soap, or a soap containing agents which bind with the calcium (soaps designed specifically for hard water).

The water spotting problem is tricky, and this is at the heart of our discussion. To prevent water spots, we have to remove the calcium salts from the surface of the car. One way to do this is to use a chamois to remove the water from the surface. The other way is to remove the calcium salt from the water. If the water is free of ions, it will leave no residue when it evaporates. This is the concept behind the deionizing cartridge in the Mr. Clean car washing system.

Let's look at the ways we can remove ions from water:

1) Distillation. Distillation is the process of evaporating and recondensing a liquid, which in this case is water. The evaporative process leaves most of the ions behind, so the resulting condensate is largely deionized. Generally the resulting water is good enough for steam irons and car batteries, but not for laboratory use. It would work for car washing, but distillation is an expensive way to remove ions.

2) Mechanical. Ions can be removed by reverse osmosis. In reverse osmosis, water is squeezed through a very fine membrane under extreme pressure. The pores in the membrane allow the water to pass, but filter out many of the ions. In practical use, the concentration of ions is greatly reduced but a significant number remain. On the plus side, reverse osmosis is relatively inexpensive.

3) Chemical. Ions can be removed by chemical reaction. This is how ordinary water softeners work. In a standard household water softener, the calcium ions are swapped for sodium or potassium ions. In this case we end up with just as many ions, but they are of a friendlier type.

Full chemical deionization comes from a two step process. You can think of it as running water through two water softeners in series. The first unit uses a chemical reaction to exchange all of the ions of one charge for the other, leaving only ions of the same charge. The second unit binds with the remaining ions and removes them from the water. This two step chemical process is capable of producing laboratory grade deionized water.

What you should know about deionized water: As the name implies, deionized water is water devoid of ions. This water is essentially an ion vacuum, just waiting to capture any unsuspecting available ions. It will strip the metal out of copper pipes, and corrode almost anything that can corrode. Deionized water is usually kept in glass or plastic containers. Special corrosion resistant faucets are used for deionized water. Drinking deionized water will remove minerals from your body. Think of it as reverse Gatorade. Drinking it in small quantities it's not going to hurt you, but it's not good for you either. The taste is very bland, since the flavor of water comes from dissolved minerals. It is pH neutral and safe for your skin, so you don't have to worry about skin contact or spray inhalation. It won't burn you like acid.

Let's get back to washing cars. Deionized water is an ideal final rinse, since it will evaporate without leaving spots. It can be used for the entire wash, but since the is an associated cost, it makes more sense to save it for the final rinse.

What is the best way to make your own deionized water? It depends on how much you need. If you are an occasional car washer, like most of us, buy a Mr. Clean system and be done with it. The cost per unit is very high, but you aren't using much, so the total cost is low.

If you use a lot of deionized water, you can do it like we do for laboratory use. The typical laboratory system uses three parts: 1) A normal water softener, 2) A reverse osmosis filter, and 3) A deionizing filter. It works like this: The water softener removes most of the calcium, which would otherwise clog the reverse osmosis unit. The reverse osmosis unit removes the bulk of the minerals using mechanical filtration. The deionizing filter completes the job by using a chemical process to remove any remaining ions.

What if your needs are somewhere in between? Maybe you do a lot of car washing, but don't want or need the expense of a reverse osmosis system. You can use a small laboratory deionizing filter without the upstream water softener and reverse osmosis unit. It will still work just fine, but the life of the filter will be greatly reduced. Still, the cost per unit is much less than using a Mr. Clean system.

Take a look at products from SpectraPure: DI ADD ON KITS AND SYSTEMS

I like the dual DI-SB-CI-10 unit. It contains two filters, each with a color indicator. The color changes as the filter is consumed. By having two filters, you can completely use up the first without risk of unfiltered water making it through the system. Once the first filter is consumed, you move the second filter to the first position, then replace the second filter. That's what I use for my laboratory deionized water. For car washing you could use a single filter, since it's no big deal if a little normal water gets through.

This SpectraPure system can be used by itself, or in conjunction with a reverse osmosis unit. There is a lot of good information on their web site.

As a final disclaimer, I am in no way related to or employed by the SpectraPrure people. I am simply one of their happy customers.

Tom