Is it harmful to water lawns with water that contains low levels of chlorine?


I am looking at reseeding my lawn. I have a lot of places that have died and turned to dirt. Watering is obviously essential. However, I have a water filtration system on my house. Filtering massive amounts of water will kill my filtration system. However, if I turn the filters off, the water has tiny amounts of chlorine in it. No one seems to be able to tell me if the chlorine will kill the lawn? The filtering system uses about one gallon of chlorine per month for all the household needs. Some articles seem to say no, where others say yes. Is that small of an amount of chlorine harmful for the lawn?


Jonathan Foster, Special Project Assistant

After doing a bit of research, I turned up three quality sources on this question:

Chlorine Toxicity, from Iowa State Univ

Watering Lawns with Chlorinated Water, from Colorado State University

Irrigation Water Quality, by Penn State Univ Extension

The three indicate turfgrass is largely unaffected by small amounts of chlorinated water, though higher levels can produce toxicity. The larger concern is that high chlorine levels can kill microorganisms in the soil, leading to pH changes and nutrient imbalances for your plants. I suspect you will be ok with the small amounts of chlorine present in your municipal water, though you could always do a small experiment of watering some with filtered and some with unfiltered water. Another great option, since you are reseeding anyway, is to get your soil tested by the UMaine Analytical Laboratory to get actual numbers on your pH and nutrient profile. If the soil test for the lawn you’ve been watering with unfiltered water looks good, it will be a strong indicator that you don’t need to worry.

I will also include a few UMaine Extension resources for lawns:

UMaine Extension Bulletin #2166, Steps to a Low-Input, Healthy Lawn

UMaine Extension Bulletin #2367, Establishing a Home Lawn in Maine

UMaine Extension Bulletin #2243, Maintaining a Home Lawn in Maine