This comes a bit late for the original author. I've spent the past 2 years perfecting a new approach for creating cleaner RSO at home. Water does play a big role later, but not during extraction.
To answer your question, No, you can't use water as a solvent for cannabinoids. Water only dissolves water soluble material which works fine for harvesting trichomes for making ROSIN cakes. But it doesn't actually strip the oils from the plant or trichomes, only a non-polar solvent would do that. Ethanol and Isopropyl are the best sovlents for the job if you don't have a lab and chemistry background. Turns out, Isopropyl has better chemical qualities for extraction than Ethanol. Isopropyl is around 25% less polar than Ethanol resulting in less contact time needed with the plant material. Downside is, both Ethanol and Isopropyl do have a polar aspect and will extract some unwanted plant material. Both are known as "untargeted solvents" meaning they dissolve what comes in contact. Oils, fats and waxes dissolve first, then come more polar items like cellulose, proteins, and phospholipids. The longer the soak, the more trash enters the solution. Oh, and this is independent of temperature, meaning Isopropyl is just as efficient at -50c as it is at 0c. Warmer temperatures allow more unwanted plant material to be dissolved so best to perform a quick cold wash to avoid impurities. But even the fastest cold wash does dissolve some unwanted materials. This is then cleaned up with Silting, Winterization and distillation using salt water, IE, Brine.
Here's a .pdf I wrote explaining the process. It is a bit technical since this is such a radically new approach. Take a look and ask any questions.
