RO units are a must have when your natural tap water's PPM/EC is sky high!
For Instance, my natural tap has an EC of .7
There's NO way in hell I can run a hydro set up and not expect bad shit to happen all through out the grow.
At an EC of .7 that means I can only feed my plants .5 of nutrients before maxing out and frying tips.
If I can only feed my plants .5 EC of nutes, then they are going to become deficient in some areas because i'm not going to be able to provide for them all the major and micro elements that they need in order to thrive…...and remember, I won't be able to "add" anything else to keep them from getting deficient because I have already maxed out.
When starting at O.O EC, I can add the maximum amount of nutrients every watering and never have to worry about deficiencies or PH going out of range.
So are RO units nonsense or crap? ABSOLUTELY NOT!!!!
Remember, anyone can just throw a plant in the ground and water it and get something from it.
But in order to really make the plant shine, you must first dial in your set up with proper water, light, temps, and air movement.