Be careful
Like many things plant size does not equal potency or quality.
I've worked with growers that went big and missed the peak. They were repotting wood.
I'd avoid as Copper Sulfate as it falls in the heavy metal and accumulates in the soil. Cannabis and Hemp being a hyperaccumulator will pull excess toxins right out of the soil and into the plant. Old orchards pose a similar problem with arsenic. In the case of Grapes and Fruit farms they have...
If your really concerned about water check out your local pharmacy or grocery, Distilled water is very cheap by the gallon. ($1.59 for gallon container)
When we ran a Miracle Grow through a Toxdetective we received a Positive result for Pesticides ( Most likely either organophosphate or Carbonates, heavy metals ) Since Cannabis is used for phytoremediation your plants may be sucking up any undesirable chemicals in the soil they are grown in.
With regard to Pesticides and Heavy Metals check out Weedscan. Not for a COA but for home growers and in process testing but very valid DIY test and inexpensive. With regard to CBD timing is often as important as any other factor. You need to harvest before the CBD begins to convert to THC
Two things regarding Cannabis is that it's not easily washed, grapes can be ( Most Pesticides are water soluble) and certain pesticides
change when burned. ( Myclobutanil can convert to Hydrogen Cyanide, prohibited in most countries, but not in the US). Also pesticide drift from non organics...