On top of the vegetables list are cucumber and lettuce, consisting of 96 percent water. Zucchini, radish and celery are comprised of 95 percent water. Ninety-four percent of tomato's weight is water, and green cabbage is 93 percent water.
I looked at the process sigma calculator (button in upper right below the search box) and they present a link to a forum post (http://www.isixsigma.com/forum/showmessage.asp?messageID=437) that gives information on calculating the sigma using a normsinv function.
The conversion is also included in some Six Sigma software, such as our Green Belt XL product. For a given sigma level, the defects per million opportunities (DPMO) is provided, assuming normality and a 1.5 sigma shift. Note that below approximately 3 sigma defects are included from both tails of the normal distribution.