Tap Water and Mineral Content for Cannabis

As we inch closer to Medical Cannabis laws being enacted, I thought it would be great to start the conversation about growing.  Where better to start than with H2O.  With the recent water situation in Flint, MI, and the similar problems around Toledo, OH– I know there is plenty of concern from growers who plan to use municipal water supplies for their legal grows.   What adulterates or chemicals might be in the tap water?  What impact will Chlorine or Ammonia residue have on my grow?  Will it throw off lab tests?

After talking with growers in Oregon and Colorado, this is a common concern, and yes, it is a valid one. Frankly, municipalities often don’t disclose the full test results of municipal water sources, and if they do, they showcase their ratings based on superficial limits they put in place.  What is a ‘safe’ amount of Lead? A ‘safe’ amount of residues?  The FDA may have one scale– but that isn’t necessarily thinking about growing (or health if we’re being honest).

Furthermore, Fracking is a real problem for ground water and water supplies in southwest and central Ohio.  You may be getting your water from a well, or some other self managed system– how are you to know the quality is up to snuff and safe to use?

The simple solutions are as follows:

– Call the extension agency and arrange for an on-site water test (for folks with self-managed systems)

– Talk with your municipality about seeing a scorecard from the latest state water tests in your area

– Worse case– go onto Amazon and get a self testing kit like this one.


Now for the specifics:

Cannabis NEEDS minerals to grow. Often, there is enough calcium and magnesium in tap water or ground water for the plant– but it often requires a bit more during flowering (get that bottle of CalMag ready).  If you deem your municipal water safe, it is still a good idea to evaporate off the Chlorine.  Simple fill your barrel or buckets, and let them sit for 24 hours.  If you have a bubbler (air stones + air pump), toss it in– it will help gently stir the water and expedite the evaporation of chemicals.  This leaves the minerals in tact, and is a pretty trusted method of acquiring safe, cheap water.  The other common method for commercial growers is to purchase a Reverse Osmosis system (We like the offerings of APEC, quality and affordability).  This has a little start-up cost and installation– but it is worth it.  It will filter out about everything in the water, all chemicals, heavy metals, even minerals.  This is often the choice for Hydroponic grow styles simply because it will allow you to 100% control the solution.  You’ll have to add back in all the essential trace minerals, but you have the control and you know what will go into your water.

I’ve heard from some growers who prefer rain water and have a barrel system.  This is awesome for a few reasons: cheap, abundant and sustainable.  But you will also need to pad it with trace minerals and depending on your location, you will need to be double sure to adjust the pH since rain water is typically a bit more acidic than tap or RO water.

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