rain and snow are not the same...the reason you would not want to use snow is...first...snow has more of a surface area giving it the ability to collect more pollution,bacteria,fungus,mold that is in the air.....second...since snow flakes float down to earth at a much slower rate then rain drops it has more time to collect all the nasty shit thats floating around.these impurities that are outside will get washed away over time...where as when you bring the snow indoors..melt it to water the plants..you are now concentrating the impurities into a smaller area and the lights are adding heat...what makes molds,fungus and bacteria grow the most...moisture and heat..theres your argument...but you will more then likely disagree and continue poisoning your plants