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How Can You Tell If Your Water is Clean?

August 3, 2016

Clean water. The U.S. population spends nearly $12 billion every year on bottled water. Brita, probably the most famous water filter manufacturer, is currently worth $350 million. Americans love clean water, and why wouldn’t we?

Most tap water contains trace amounts of stuff we don’t want in our bodies. Metallic ions, residue, salts, and other contaminants from industry, agriculture and sewage all show up in our tap water. Of course, tap is safe to drink in most places – safe for humans, that is.

Plants require special attention. When it comes to a cannabis crop, having the cleanest water possible ensures that you’re feeding your plants the best they can get.

Why it’s a problem

When it comes to salts in the water, impure sources can complicate feeding and fertilizing. Most commercial fertilizers use nitrogen- and phosphorus-based salts. If there’s already salt residue in your water supply, it can add to any salt made by the fertilizer. Too much salt will wreak havoc on your plants’ health, causing things like fertilizer burn.

Too much pH or alkalinity can also compromise a grow. Cannabis thrives at a specific pH—about 6.0 to 6.5, which is slightly acidic. This environment enhances the absorptivity of nutrients and minerals, requiring less energy from your plant and less input from you, the professional grower, in the long-run.

Heavy metals like cobalt or iron can potentially compromise some medical patients. Remember that cannabis draws up everything from the water, including metallic ions. Most of these metals will be transported into the fan leaves. Patients who’ve already been exposed to heavy metals, whether by pollution or chemotherapy, could grow more ill if there’s significant metal residue in their plants. Immuno-compromised patients could also face health complications from metals.

Testing the water and fixing it

Any chemical issues that arise from unclean water can usually be tested with simple at-home kits. Strips meant for hot tubs and swimming pools double as affordable yet accurate testers for your cannabis grow, too. These measure pH, chlorine levels and other components of your water supply.

For a fee (anywhere from $20 to $200), you can submit samples of your tap water for professional testing at a lab. State labs can perform these tests, too, but doing them at a private lab will ensure your results are confidential and custom-tailored to your request.

If your water tests unclean, there are ways to fix it. Ordering gallons upon gallons of bottled water isn’t the most efficient way to get clean water into your plants. Your best bet is to invest in system that cleans your tap water. This way you can simply run a hose into your grow operation, pass it through the machine…and out comes pure water.

The only rule to remember is that water is different everywhere. Water in San Diego has different issues compared to water in Colorado Springs, Colo. Pick the best water filtration method based on where you live and what your needs are.

Reverse Osmosis

The most popular and one of the most trusted ways to clean your water is with a reverse osmosis (R/O) kit. It works by passing the water through a semi-permeable membrane, blocking out the bad chemicals while allowing pure water to pass through. Usually these systems include an additional carbon filter to remove anything missed during the first pass. A quality filter will run you anywhere between $1,000-$1,500; much larger systems can cost as much as $10,000.

Besides cost, the one downside to R/O is that most systems don’t remove chloramine. Chloramine levels in most tap water won’t affect soil-medium grows, but they can cause headaches for hydro grows. In that case, you can usually purchase a separate add-on filter for your R/O system to remove chloramine.

Furthermore, reverse osmosis can be somewhat wasteful and slow to use. The typical point-of-use system produces roughly 1 gallon of clean water every hour, and wastes 2 to 3 gallons for every gallon it cleans.


If it’s good enough for booze, it must be good enough for cannabis grows, too, right? Distillation heats the water over a coil, causing it to turn in to steam. The steam condenses and cools, becoming cleaner water. Distillation is great for removing metals from the water, as well as killing most bacteria and other microorganisms. However, distillation doesn’t get rid of many organic or volatile compounds, such as petroleum-based chemicals. Like reverse osmosis, point-of-use distillation is a slow process. Quality distillation systems should always include a carbon filter.

Carbon Filters Alone

If the water in your area tends to be fairly clean already, then a carbon filter may be enough to get the job done. These filters use carbon materials to trap any unwanted chemicals in the water supply. They can be constructed from makeshift set-ups for just a hundred dollars, to more elaborate contraptions that can reach $1,000. Since carbon filter systems are relatively simple, they tend to be much cheaper solutions when compared to reverse osmosis.

Only 1 gallon per hour?

Most commercial filtration systems clean about 1 gallon of water per hour. That may not sound like a lot, because it isn’t. However, higher-end equipment can process water faster than this. You can also combine multiple systems to filter more water at one time. Just be sure you calculate how much water you need for any given day, and have that water on reserve in storage tanks.

Rest assured, most areas in the U.S. have water safe for both human and plant consumption. Be sure to check with local water reports, usually provided by your city offices. Hydro grows are much more dependent on clean water than soil or other organic media. Remember that water in nature contains trace minerals and salts, and avoid excessively cleaning your water sources.


By Randy Robinson
Image Credit: By Marlon Felippe (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 4.0-3.0-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/4.0-3.0-2.5-2.0-1.0)], via Wikimedia Commons
Cannabis Cultivation Today articles are for informational purposes only and should not be considered legal guidance or advice on grow practices. You should contact an attorney or a qualified cultivation consultant for specific compliance and cultivation advice.

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