Dont forget this method is being preached by someone that uses hardware store grade acetone to make extracts. Take what he says with a grain of salt.
It's pure enough. There's actually a lot more crud in tap water. There's also a lot more in nutrient solutions and the resulting plant material. It's also low toxicity. Hardware store acetone is the same as any other. It's all made the same way. It's just in a can instead of a bottle.
"Acetone can be found as an ingredient in a variety of consumer products ranging from cosmetics to processed and unprocessed foods. Acetone has been rated as a GRAS (Generally Recognized as Safe) substance when present in beverages, baked goods, deserts, and preserves at concentrations ranging from 5 to 8 mg/L (Oser and Ford, 1973). It can also be detected in measurable amounts in onions, grapes, cauliflower, tomatoes, milk, cheese, beans, peas, and other natural foods. Milk from dairy cattle may contain very high levels of acetone, ranging as high as 225 mg/L for the milk from hyperketo-nemic cows (Andersson and Lundström, 1984). Acetone has also been identified, but not quantified, in air samples from numerous plants and microorganisms. In addition to its elimination in the expired air of all mammals, acetone is excreted as a metabolic end-product by some bacteria (Clostridium butylicium), molds, fungi (Paecilaomyces variotii), and algae (Cryptomonas ovata palustris) (George et al., 1983; Sunnesson et al., 1996; Collins and Kalnins, 1966)."
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