The Missouri Water Problem: Should You Be Filtering Your Tap for Your Cannabis Plants?

Missouri may be home to world-famous springs and rivers, but when it comes to watering your cannabis crop, the story’s a little more complicated. If you're a homegrower relying on city or well water, there's a good chance your tap contains more than just H₂O—and some of those hidden extras could be harming your plants.

Whether you're growing indoors in St. Louis or out back in the Ozarks, this guide explains why Missouri water isn’t always cannabis-friendly, how to test and treat it, and when filtering your tap water could make the difference between sad leaves and sticky buds.

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What's in Missouri Tap Water, Anyway?

Tap water in Missouri varies significantly depending on where you live and your water source.

Common water types across the state:

• City water (chlorinated and fluoridated): Found in metro areas like Kansas City, Springfield, and Columbia

• Rural well water (often high in iron, calcium, or sulfur): Common in southern Missouri and farm country

• Spring-fed or rural community systems: Sometimes untreated, sometimes heavily treated—depends on the provider

While it's safe for human consumption, Missouri tap water often contains hard minerals, chlorine, chloramine, and sediment—all of which can build up in your soil, block nutrient uptake, or stress delicate cannabis roots.

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Common Problems Missouri Growers Face with Unfiltered Tap

Hard Water (High Calcium and Magnesium)

Most of Missouri has moderately to very hard water, especially in the northern and western parts of the state. While cannabis plants need calcium and magnesium, excess amounts can lock out other nutrients, especially potassium and iron.

Symptoms of hard water stress:

• Brown leaf edges or rust spots

• Slow or uneven growth

• High runoff pH readings (above 7.0)

Chlorine and Chloramine

City water supplies often use chlorine or chloramine to disinfect. While chlorine can dissipate with time, chloramine is stable and doesn’t evaporate. Both can:

• Damage beneficial microbes in your soil or compost teas

• Cause root stress, especially in seedlings and clones

Iron, Sulfur, and Sediment (from Well Water)

Unfiltered well water in Missouri can contain:

• Iron: Leads to red/brown staining and may block phosphorus

• Sulfur: Causes rotten egg smell and pH swings

• Sediment: Clogs drip lines and reduces oxygen around roots

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Should You Filter Your Water?

The short answer: probably yes—especially if you’re seeing stunted growth, nutrient issues, or high pH runoff without a clear explanation.

But don’t guess. Start by testing your water.

Step 1: Get a Water Test

Use a local extension office (like the University of Missouri Extension) or buy a home water test kit that covers:

• pH

• Total dissolved solids (TDS/PPM)

• Hardness

• Chlorine and chloramine levels

• Iron and sulfur content

If your water is above 200 PPM out of the tap, it’s time to consider treatment.

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Water Filtering Options for Missouri Growers

Let It Sit (Chlorine Only)

• If your city water only contains chlorine (not chloramine), fill a bucket and let it sit uncovered for 24–48 hours.

• Add airstones to speed up chlorine evaporation.

• Not effective for chloramine.

Use a Carbon Filter

• Removes chlorine, chloramine, and some sediment.

• Great for indoor or small tent growers.

• Inexpensive and easy to attach to a hose or sink.

Reverse Osmosis (RO) System

• Removes 90–99% of all dissolved solids, including salts, minerals, and chemicals.

• Best for hard water or sensitive grows (hydroponics, living soil, autoflowers).

• Downside: RO strips out all minerals—so you’ll need to re-add calcium and magnesium (Cal-Mag).

Inline Hose Filters

• Ideal for outdoor growers using tap water.

• Filters chlorine, heavy metals, and some minerals.

• Doesn’t waste water like RO and is easy to install on a garden hose.

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Bonus Tip: Adjusting pH After Filtering

Even filtered Missouri water may come out too alkaline for cannabis. Ideal water pH is:

• 6.0–6.5 for soil

• 5.8–6.2 for coco or hydro

Use a pH down solution (like phosphoric acid or citric acid) after filtering, especially with RO systems.

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Can I Just Use Rainwater?

Missouri growers have a secret weapon: abundant rainfall in spring and early summer. Rainwater is soft, clean, and perfect for cannabis—but it still needs basic treatment.

Do this before using:

• Filter through mesh or cloth to remove debris

• Store in clean, shaded containers

• Test pH before use (can fluctuate with storm activity)

If you’re harvesting rain off a shingled roof, avoid early runoff to reduce chemical residue. First flush it, then collect.

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Growers Who Filter, Harvest Better

Filtering your water may seem like a hassle, but it’s one of the most overlooked upgrades Missouri growers can make. Clean, properly balanced water helps your plants:

• Uptake nutrients more efficiently

• Avoid lockouts and buildup

• Thrive in native soils or containers

• Deliver smoother, cleaner-tasting flower

Whether you’re dealing with city chemicals or well water surprises, a simple filter could turn around an entire grow.

At HomeGrow Helpline, our mission is simple: to help home cultivators across the state navigate the unique challenges of growing legal weed