Why Dechlorinating Tap Water Matters in Hydroponics

Why Chlorine in Tap Water Is a Hidden Problem for Hydroponics

Most growers don’t think twice about filling their reservoirs with tap water. But here’s the catch: municipal water isn’t just H₂O. It’s treated with chlorine and chloramines to kill bacteria and pathogens. Great for safe drinking water, but potentially harmful for your plants and beneficial microbes.

In hydroponics and living systems, chlorine can:

• Damage delicate root hairs.
• Suppress beneficial microbial life.
• Disrupt enzyme activity.
• Cause leaf burn, stunted growth, or even chlorine toxicity in sensitive crops.

Crops Most Sensitive to Chlorine

Some plants are particularly vulnerable, including:

• Leafy greens like lettuce and spinach
• Strawberries and grapes
• Avocados
• Orchids and many tropical plants

Even at low levels, these crops may show stress from chlorinated water.

Global Variations in Tap Water Chlorine

Not all tap water is the same. Chlorine levels vary by region:

• USA (Las Vegas, Southern California): Known for high chlorine/chloramine levels, often over 4 ppm.
• Australia (Perth, Sydney): Elevated chlorination reported.
• UK: Lower chlorine levels thanks to cooler water and frequent rainfall, but still present.
• Southeast Asia/India: Heavy chlorination often used after monsoon season.

Knowing your local water quality is the first step toward protecting your crops.

How to Dechlorinate Tap Water for Hydroponics

Here are proven methods to make your water plant-friendly:

1. Let It Sit – Leave water for 24–48 hours for chlorine to evaporate. (Doesn’t work for chloramine.)
2. Aeration – Use an air stone to speed up off-gassing.
3. Activated Carbon Filters – Remove both chlorine and chloramine while also reducing heavy metals and pesticides.
4. Vitamin C Treatments – Neutralize chlorine, though they degrade over time.
5. Reverse Osmosis (RO) or Spring Water – Provides pure water, though RO wastes some water.
6. Specialized Dechlorinators – Products like Eutrema’s Dechlorinator. Alternatively use Liquid Gold as your fertiliser, which includes dechlorination technology in the formulation.

Why It’s Crucial for Living Systems

Even if you’re not using soil, many hydroponic systems rely on living biology:

• Aquaponics bacteria that process fish waste.
• Mycorrhizae and microbial inoculants added to substrates.
• Compost teas and biofertilizers for natural nutrient cycling.

Chlorine wipes out these beneficial microbes before they can work. Dechlorinating your water preserves their effectiveness and keeps your root zone thriving.

Quick DIY Test for Chlorine

You can test chlorine levels easily with DPD tablets (available online). Drop one in a sample of your tap water:

• If it turns pink, chlorine is present.
• Add your dechlorinator—if it clears instantly, you’re good to go.

Final Thoughts

Dechlorination might seem like a small step, but it can have a big impact on plant health, yields, and microbial life in your hydroponic system. Whether you’re growing leafy greens, fruiting crops, or tropical plants, removing chlorine is an easy win for healthier, more resilient plants.

So next time you top up your reservoir, make sure your water is chlorine-free. Your plants—and microbes—will thank you.

Article by Dr Russell Sharp

If you would like to keep up to date with subjects just like this, you can listen to both our podcasts! Links can be found bellow:

Hydroponics Daily Podcast: https://podcasts.apple.com/us/podcast/hydroponics-daily/id1788172771

Cereal Killers Podcast: https://podcasts.apple.com/us/podcast/cereal-killers/id1695783663