Irrigation: How much water does cannabis use?

Cannabis uses more water than the average crop. Poor irrigation technique can increase that consumption tenfold! Yet water is seldom a limiting factor or major financial concern for cannabis farmers. A small personal garden uses a few toilet-flushes worth of water per day. A modest warehouse can function on truck-hauled water.

For the consumer, this works out to about a quart of water per gram purchased. That number is easy to remember because most people drink about a quart of water after smoking a one gram joint.

For the producer, this equals roughly 500 gallons per light, per year. Inefficient irrigation technique increases water consumption tenfold. For a 100 light warehouse facility, this is the difference between .15 and 1.5 acre feet of water per year! That’s about the same consumption as a couple of suburban homes.

A water-wise indoor garden will use about 8 oz./sq ft of plant canopy, per day. An inefficient drain to waste garden could use up to 1/2 gallon/sq ft per day. That's out to about a quart of water per plant/day at a density of six plants per light, on the low end.

Drain to waste hydroponics waste the most water because it produces significant runoff that isn’t recaptured. Recirculating hydroponic systems seem efficient; however, reservoir maintenance requires frequent discharge and replacement of the entire container volume. Either is more efficient than conventional agriculture, but there are ways to save if you are concerned about water consumption.

Sensor-controlled drip irrigation is the most efficient irrigation technique. Patient hand watering is comparable. We really like the drip irrigation system because it is simple, analog and gravity-fed.

Roots seek water from a Tropf Blumat drip irrigation system.

Avoid these water-wasting mistakes:

• Too hot in the grow room.

• Too dry.

• High vapor pressure deficit.

• Rootbound plants.

• Over-watering.

• Hand-watering too quickly.

The number one cause of wasted water is multi-tasking while a hose is on. Don’t believe a grower who says they don’t accidentally overflow their reservoir now and then! Perhaps you even have a hose on right now? Check your valves, then focus on more critical money-saving efficiencies, like reducing your electric bill.