IKIK, tldr but..
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Q: There's been talk about local water suppliers treating water with chloramine instead of chlorine. The proponents of this process seem to say there is little detrimental effect. But I read on one web site that chloramine "does nasty things to microbes in soil." Do you have any information on what this will mean to gardeners?
A: Excellent question. The point of using chloramines (a combination of chlorine and ammonia) is to kill harmful bacteria in drinking water, so it's logical to assume that irrigating plants with chloraminated water will do some damage to bacteria in the soil - including bacteria helpful to plant growth.
The question is whether it's going to do enough damage to cause plant problems. My gut feeling is no - with a couple of caveats and possible exceptions. Some thoughts that struck me while wading through the research...
1.) Chloraminated water has been used for at least 90 years in the U.S. and abroad. If it was going to cause trouble in the garden, someone should have noticed by now. Here's what one study from Australia's Urban Water Research Association concluded: "It seems unlikely that the use of chloraminated water for irrigation of soil-grown plants would have adverse effects on growth, whether the water is applied directly to the soil or as an aerial spray."
2.) Soil-borne bacteria are pretty resilient and plentiful. The chloramine levels used in treated water shouldn't make more than a dent in the soil bacteria population. And I suspect the bacteria would quickly bounce back.
3.) Any ill effects would depend on how much chloraminated water you applied and how often you applied it. Rain would dilute and leach the chloramine out of the root zone, so plant damage (if any) would be more likely in droughty weather. I'd be more concerned about container plants, which would get daily and focused doses of chloramine throughout the growing season. Symptoms would be browning around the leaf edges and possibly yellowing of the leaves.
4.) The other area of concern is in water gardens. Fish are sensitive to chloramine as well as chlorine. But unlike chlorine that dissipates in a day or two, chloramine persists longer (a trait that also makes it more attractive in treating drinking water). If you're lightly topping a pond with chloraminated water - say, by less than 5 percent of volume - you're unlikely to harm fish. But if you're replacing the water or adding more than 5 percent, you should go to the pet store or pond supplier and buy a product that neutralizes chloramine. Carbon and biological filters also gradually remove the ammonia that's a component of chloramine.
5.) If you're making compost tea with chloraminated water, that's likely to destroy some of the bacteria, which is one of the main benefits of this fertilizer in the first place. You can neutralize the chloramine by mixing 1 teaspoon of humic acid per 100 gallons of compost tea, according to one company that makes compost-tea brewers.
A good way to sidestep this whole issue is to collect your own rain water and use that as much as possible. Also helpful would be adding compost regularly to your soil, which is loaded with beneficial microorganisms.""
