Most people’s concern seems to be a high concentration of microbiological contaminates; viruses, bacteria, etc. I clean regularly with bleach (weekly min.) I know most of it is due to rain water which is extremely clean and transpiration from the plants.
It’s a brand new unit as well. Where I live water is free but I don’t like to waste water.
I’m adding another R/o filter and tank to run off my water transfer pumps out my reservoirs to pull out the leftover nutrients and reuse the water.
I start a set on flush Saturday and I’ll test it out.