I have worked with industrial ro/di systems and from this I know you need to be careful what the water is stored in. Also, it is easy to contaminate this water.
There is interesting debate on the good or bad in drinking 'pure' water for humans. Without getting to scientific, very pure water doesn't want to remain pure and will 'attack' minerals to make it more neutral. Some believe this is helpful to remove impurities in our bodies. The reality is, if you have undigested or partially digested material in your small intestine....the 'pure' water will take what it needs from this material. What will happen in an empty snake stomach? I don't know.
IMO I would stick to the evap method for watering my critters.