Grow Tip: Don’t Filter Your Water Using Reverse Osmosis

Jeff Standley

Grow bibles all recommend using filtered water for obvious reasons, but be careful picking your filtration method. Any reverse osmosis water filtration unit smaller than an industrial-scale unit wastes three to seven times the clean water it delivers! Especially if you live in a drought-stricken state like California, you should use RO’s water-efficient alternative: whole-house activated carbon filtration.

After decades of industrial dumping, most of the nation’s water supply is contaminated with heavy metals and persistent organic contaminants. Even if your tap water happens to be safe enough to drink, as is the case in most of the country, your water will still contain a minimum level of chlorine. To be exact, chlorine in the water comes in the form of chloramine. Municipal water treatment centers inject a mixture of chlorine gas and ammonia, which react to form chloramine.

Chloramine does not evaporate as readily from water as does chlorine. This is annoying for people who want to remove chlorine without having to filter, but be thankful for this. Chloramine’s poor rate of evaporation means its disinfecting properties stick around for longer, meaning won’t get sick from some water that’s been sitting around in a water main for a week.

Why do growers want to remove chlorine (ahem, chloramine) from their water? Chlorine kills microbes, a property that presents a serious issue for growers that take advantage of beneficial fungi and bacteria. Some evidence also indicates that chlorine in any form may stunt root growth in plants. Chlorine also reacts with organic compounds present in tap water to form trihalomethanes, toxic chemicals that can also stunt plant growth, be toxic to beneficial microbes and may even accumulate in the cannabis buds that you end up smoking.

Despite all the toxic warnings presented about the potential dangers of chlorine and its byproducts, one type of water filtration can do more harm than good; not harm to you, but to your local water supply. Specifically, small-scale reverse osmosis water filtration units waster immense amounts of water for each gallon of clean water they deliver.

Reverse osmosis uses high pressure to force the natural process of osmosis to happen in reverse. Normally, water molecules flow from one side of a semipermeable membrane that has a low concentration of solutes (the contaminant) to the side that has a high level of solute. Without any input of energy, the two sides would eventually equilibrate until both sides have an equal concentration. In reverse osmosis, the system uses high pressure to form the natural process to happen in reverse, meaning clean water flows from the dirty side to the clean side. However, water needs to continue to flow on both sides for the process to work, meaning some water is always wasted.

Industrial-sized reverse osmosis systems can create extremely high pressures meaning very little water flows to waste, and up to 90% can get recovered. Small, under-sink an even whole-house units can’t generate nearly the same amount of pressure, and only recover around 15% of the water they consume; the rest goes to waste.

An alternative to this wasteful system is the whole house activated carbon filter for watering cannabis with clean H2O. You can imagine this as a giant filter pitcher; water comes in chlorinated, and leaves de-chlorinated.

A state like California can barely afford the efficient water usage from crop cultivation, let alone an inefficient usage! Don’t invest in a home reverse osmosis unit; go for the carbon. If you already have one, get rid of it; the planet can’t afford you wasting that much water.

Credits: Buds from Capital City Cannabis Company;  photo by CannaBusinessWA’s Jeff Standley

  1. Britta then stir, 1st to the right, then to the left. Structured water is best. I do for intent not belief. My intentions are pure.

  2. Watts makes a residential under sink Reverse Osmosis filter that recycles the unused water back into the hot water line. If you already have a ro system repurpose the water by running the drain to a drum and water the grass or wash your car with the water. It’s important to know that a whole house activated carbon filter is not going to come close to the level of filtration you get with reverse osmosis. That being said the two work well together, the whole house filter will provide a level of filtration for any water needs, and the ro can be a higher level of filtration used for drinking water, and watering plants;)

    1. Lovely sentiment, and people should absolutely show concern for the environment and water usage. But, unless you’re a vegan as I am, you waste hundreds of times more water than even using ro constantly all day. A single 1/4lb burger takes 2500-3500 gallons of water to produce. One burger. Are you willing to cut out meat eggs and dairy for your love of the environment? Dont be a hypocrite.

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