The process of reverse osmosis takes almost everything out of the water right down to bacteria level. The advantage of ROwater is that it gives you control over what you feeding your plants. Once you have pure water you can add to it whatever your plants need. Many geen houses use this technique as it stops the build up of salts in the soil, and therfore prolongs the life of the soil (no need to re-pot!). I hope this is of some use.