Colorado Water Quality and Cannabis: What’s Really in Your Tap?

Growing cannabis indoors in Colorado has plenty of perks - plentiful sunlight outside, legal freedom, and a thriving community of growers. But one factor often gets overlooked, especially by new cultivators: your tap water. What flows from your faucet could be quietly shaping the success (or struggles) of your grow. Let’s dive into what’s really in Colorado’s water and how it affects your cannabis plants.

Why Water Quality Matters in Indoor Cannabis Growing

Cannabis is incredibly sensitive to what it’s fed - especially in a hydroponic or soil-based indoor setup. Tap water carries more than just H₂O. It can include dissolved minerals, chlorine, chloramine, heavy metals, and varying pH levels. Over time, these can:

• Disrupt nutrient uptake
• Alter soil biology
• Cause pH imbalances
• Contribute to salt buildup

In short, poor water quality can stunt growth, damage roots, or even kill your plants if left unaddressed.

What’s in Colorado Tap Water?

Colorado’s water sources vary depending on your city or region, but here are the common elements you’ll likely find:

1. Chlorine and Chloramine

These disinfectants are added to kill bacteria in municipal water systems. Chlorine will evaporate if water is left out, but chloramine (a mix of chlorine and ammonia) is more stable and harder to remove.

Problem: These compounds can destroy beneficial microbes in your soil or root zone - especially in living soil or organic grows.
Fix: Use a carbon filter or reverse osmosis (RO) system, or treat water with ascorbic acid (vitamin C) to neutralize chloramine.

2. Hardness (Calcium & Magnesium)

Colorado water is often moderately to very hard, depending on the area. This means it contains high levels of calcium and magnesium.

Problem: While these are essential nutrients, too much can lock out others like potassium or iron, and leave crusty buildup in your grow equipment.
Fix: Consider using an RO system if your water tests high in hardness. You can reintroduce controlled amounts of calcium and magnesium through supplements.

3. pH Levels

Colorado tap water typically runs alkaline, with a pH around 7.5 to 8.5 - too high for cannabis, which prefers 5.8 to 6.5 in soil and hydro systems.

Problem: High pH can lead to nutrient lockout, causing deficiencies in iron, manganese, and phosphorus.
Fix: Always test your water and adjust with pH down solutions before feeding your plants.

4. Total Dissolved Solids (TDS)

TDS measures the concentration of minerals in water, usually in parts per million (PPM). Most Colorado tap water ranges from 150–400 PPM.

Problem: High TDS can overload your soil or hydro system with unaccounted nutrients, making it harder to control your feeding schedule.
Fix: Use a TDS meter to check your levels. If you’re over 250 PPM, consider diluting with RO water or using RO exclusively.

Testing Your Water: What Every Colorado Grower Should Do

If you haven’t tested your water yet, it’s time. You can use:

• TDS meter (cheap and fast)
• pH meter or test strips
• Water report from your city (available online)
• Comprehensive water test kits for chlorine, chloramine, heavy metals, and more

Pro tip: Test both your tap water and your runoff to see how your soil or system is influencing water quality over time.

Best Water Practices for Colorado Indoor Grows

Here’s a quick breakdown of smart water habits:

• Let tap water sit 24 hours (if you're only dealing with chlorine)
• Use filtered or RO water if you see issues with buildup, pH, or nutrient lockout
• Reintroduce beneficial minerals after filtration (especially in RO systems)
• Keep water temperatures stable, ideally between 65–70°F
• Avoid overwatering, especially in low-humidity Colorado homes

Grow Smarter, Water Wiser

Colorado growers are lucky to live in a state with relatively clean water - but “clean” doesn’t always mean “cannabis-friendly.” Paying attention to what’s in your tap can mean the difference between a stressed-out plant and a thriving harvest. With a little testing and some minor adjustments, you can make your water work for your grow - not against it.

We're HomeGrow Helpline and we’re passionate about helping Colorado home growers succeed, one healthy plant at a time. From beginner tips to deep-dive grow guides, we’ve got your back - no matter what’s in your water. Call or text us at (937) 476-1669.