I don't have an answer, but you may want to also consider the crackle test. Put a few drops of oil in an old spoon and hold a flame under it. If it just smokes, no water. If it crackles, water is present. You may find more info on the crackle test by searching at NORIA.com.
This NORIA article tells about field testing for glycol. Scroll down for the blotter spot test. Especially click on Fig 5 in the article. It is a series of blotters where they purposefully added glycol. You could use the blotter as a pre-screen to help determine when it is time to send in the sample for lab analysis.
This NORIA article discusses the crackle test. Note I use a butane lighter under a spoon, not a hot plate as in the article. Of course, water may burn off and the glycol remain, so my initial advice was probably not the greatest, but can't hurt.