Conserving massive amounts of water when cultivating cannabis in Los Angeles is almost as easy as turning on the tap.
Cultivating cannabis indoors offers a big environmental bonus: water conservation. In Los Angeles, our municipal water supply is pretty good for growing, which is a huge advantage for us.
In a lot of places, municipal water comes out of the tap with a TDS (total dissolved solids) ratio of anywhere between 360 and 460 parts per million. But further filtering produces its own problems. The issue is with reverse osmosis and the amount of waste it can produce. I’ve spent many hours, depressed, watching wastewater run out while filtered water slowly trickled up. Throw in a multiyear drought, and the guilt starts to run deep.
However, if you combine the decent municipal water we have in Los Angeles with the zero-ppm condensation coming out of your air handlers, you’ll find a recipe for water with a base ppm of 120-250. Approximately 3,000 square feet of canopy consumes about 140 gallons of water per day from the tap. That’s less than an individual person uses in a day.
One problem that arises with this method—something you’ll have noticed if you’ve ever looked at a dehumidifier reservoir—is the accumulation of gray algae. Once algae gets a start, it will accumulate until it robs your plant roots of oxygen. Gray algae also attract fungal gnats by the horde.
Sterilization is the answer. I recommend using two sets of pumps for your air handlers, switching them out every couple of weeks and sanitizing them by soaking in a bleach solution. You will also want to run 3/8-inch lines between the pumps and reservoir to collect reclaimed water, which will need to be switched out monthly, or you can blast pressurized air through the pumps while they’re dry to make sure any residual gray algae is purged. You’ll also want your HVAC professional to install UV lighting in the air handlers. This will be the first line of defense against gray algae.
For the reservoir you initially pump the reclaimed water into, you also want to set up a second water line with another UV purifier (inline) that finally pumps to your clean reservoir. It’s a bit of a process, but it doesn’t cost that much in the long run and will get you off the reverse-osmosis water-filtration machines.
In my experience, you’ll get about 2.6 gallons a day of zero ppm water per ton of air conditioning. So, if you’re using 50 tons of A/C total, you’re reclaiming 130 gallons of water a day with zero ppm. Mix it with your tap water, and you’ll be crushing it environmentally.
Erik Hultstrom has cultivated and advises cultivators in Southern California, and sits on an advisory panel with the Public Utilities Commission in California. He is founder and president of the Cultivators Alliance, an organization of indoor cultivators in Southern California, and is a board member of the Southern California Coalition.