Back in October 2007, we wrote about how significant water is to life, and how hydrogen-bonding intermolecular forces enable that. Essential as it is, however, water alone isn't sufficient for cleaning work. We have to add something to it, or take something away.

Since 1974, the U.S. has had Federal standards for drinking water which have the force of law. Generally, the Safe Drinking Water Act (SDWA, 40 CFR-141) specifies what must not be found in water at all, and the maximum permissible levels at which other impurities can be found. This is a basic level of water quality to which substantial changes are made to enable it to be used in industrial operations.

METAL CLEANING TECHNOLOGY
Typical aqueous cleaning technology starts with water which would comply with the SDWA and then adds something. There are two reasons for this: most surfaces we want to clean have significant hydrocarbon character, and hydrocarbons aren't soluble in water.

So we have to add something which is compatible with both water and the materials we want to clean. That's a surfactant — a bifunctional molecule. An example of such is shown below.

If water weren't so cheap (well, it once was so), so commonly available (also once was so), and innocuous (to humans and the environment), we could do this cleaning work with another base fluid to which we add some bi-functional molecule.