Chlorine and Chloramine in Water for Cannabis Plants

We checked the nutrients. We checked the pH. The plants still kept falling apart. The clue wasn’t another bottle on the shelf. It was in the local water report: chloramine.

The video follows that frustrating case and the recovery after the water source changed. Here’s the part worth understanding before you blame your own tap.

Same job. Different chemistry.

Water companies add disinfectants to control germs. Free chlorine and chloramine do that job differently. Free chlorine can decline as water stands, but chloramine lasts much longer. Leaving a bucket out overnight is not a reliable way to remove chloramine. [1] [2]

The chemistry isn’t as complicated as the names make it sound. Chlorine gas is Cl₂, but in treated water, free chlorine is mainly HOCl and OCl⁻. Monochloramine is NH₂Cl: one nitrogen, two hydrogens and one chlorine. That small change makes a big difference to persistence. [3] [4]

Simple solution: let chlorine dissipate

If your water uses free chlorine, letting it stand exposed to air can reduce it over time. People call this letting chlorine evaporate. However, Chloramine does not disappear this way. [9]

Peroxide reacts with free chlorine; it does not simply speed up evaporation. [10]

What happens around the roots?

Disinfectants don’t know which microbes you want to keep. At sufficient exposure, they can damage microbial proteins and disrupt cell function. Roots can also be injured. Controlled hydroponic lettuce studies linked chloramine to root browning and reduced growth, with both concentration and exposure time affecting the result. [5] [6] [7]

Soil changes the picture. Organic matter reacts with disinfectants, and microbes live in a complicated network of pores and surfaces. In a wheat-soil experiment, chlorine caused some microbial changes, but many responses recovered and the soil was not sterilized. Although chlorine may kill bad microbes, it does not discriminate and will kill good microbes as well. [7] [8]

Read the report before buying the fix

Start with your water utility’s current water-quality report and look for chlorine or chloramine. A test that measures free and total chlorine can help check what reaches your tap and what remains after treatment. A pH or PPM reading alone cannot tell you whether chloramine is present.

For removal, check the exact product’s chloramine-reduction claim. Suitable carbon treatment or a compatible neutralizer can work, but not every filter has that capability. An RO membrane alone isn’t the answer; a complete RO system may depend on its carbon stages for this job. Follow the product label and verify the result. [2] [4]

My takeaway: don’t keep changing nutrients while ignoring the water they go into. But don’t diagnose chloramine from a brown root or a yellow leaf alone, either. This is one grower’s experience.

For the other numbers on that report, see the pH, EC and PPM guide. You can also return to the interactive cheat sheet.

Water-treatment products

Chlorine/chloramine conditionerA simple small-batch option when the product label confirms compatibility with your grow system. Dose from the label and verify the treated water.View product

Multi-stage RO systemUseful when hardness or source-water EC also needs to come down. Confirm the carbon stage is rated for chloramine and service it before capacity is exhausted.View product

Affiliate disclosure: HWGrow may earn a commission from qualifying purchases at no additional cost to you. Verify that any treatment product is rated for the disinfectant, flow rate and grow system you use.

Updated October 22, 2026.