>It is best to have low heat and large surface area to facilitate
>rapid evaporation of the low volitility solvent water.
Close. It's best to have as high of a heat as possible and a large surface area. No matter the heat, you're going to have the codeine held at a temperature of 100C. The idea is to minimize the time that it stays at 100C, so the higher the heat, the faster the water boils off, the less time the codeine is at 100C.
Water is the best solvent, don't let your intuition get in the way. I thought alcohols, organics, etc would be better. They're not... extract with water (if you want better purity, use distilled water).