There is a not so subtle reason why cannabis waste is turned into water or other inert ingredients. Canada and most US states require that waste from cannabis production require that discharged material have no more than 50% cannabis related product (some States are more restrictive) and be tested for that level of compliance.
The problem with cannabis production is that you need to treat water and the plant material separately to comply with these requirements. You also can't mix cannabis waste with other organic waste.
Before anyone asks I might know this because I may have stretched a few laws in the 1970's.
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