#AskAChemist: The LA treatment

This is the first installment of Ask A Chemist. Here’s a question received from LA peep @SurlyAmy

L.A. Valley is switching from chlorine to chloramine to clean up the water system (which will also make tastier water) and of course people are FREAKING OUT. Some people are even sending emails in ALL CAPS. What’s the deal?

‘Tis true, various LA County Waterworks Districts (LACWDs) are ditching chlorine for chloramines.

When talking water treatment, the chloramine in question is monochloramine.  What’s this new-fangled chemical monochloramine? It’s not new. Monochloramine has been used to treat water for about a century in the US, Canada, and the UK. According to the EPA, 1 in 5 Americans currently enjoys monochloramine treated water.

We treat water with chlorine and/or monochloramine to keep nasty stuff (like SalmonellaCampylobacter, and norovirus) from coming out of our faucet along with water. Chlorine does a super good job – it’s like the Jason Statham of germ-killing additives. Why, then, would we use monochloramine over Statham chlorine? Well, chlorine in our water reacts with some natural organic matter* that’s in our water to make some so-called “disinfection byproducts” (DBPs). Some of these DBPs are not-so-nice, so we regulate them. We’ve got to keep these DBPs’ formation and concentrations in check – monitoring levels, adjusting treatment regimes, etc. These regulated DBPs are why LA is switching to chloramines. Straight from LA County’s Department of Public Works Chloramines FAQs

Why are LADWP and the Los Angeles County Waterworks District No. 21 converting to chloramines for disinfection?

A: Chlorine reacts with naturally-occurring organic material found in surface water, forming disinfection by-products. Recently, the water quality standard for disinfection by-products was made more stringent by the U.S. EPA and the State. The new standard was prompted by studies linking the chlorine disinfection by-products to higher risk of cancer. To comply with the more stringent standard, LADWP had to change its disinfectant to chloramines.

Practice and available research shows that “[c]ompared to chlorine, water treated with monochloramine contains fewer regulated disinfection byproducts that have been linked to human health problems.”

Is monochloramine a second Statham? Quick, lethal, gone? Sorta. Monochloramine is lethal to the nasty stuff we’re aiming for, though it takes longer to kill the stuff. Kinda like Statham in Transporter 2. Monochloramine sticks around longer than chlorine. Which is sorta of a good thing… you never know when you’ll need to make a sequel. Or kill more nasty stuff in our water.

Statham is just trying to transport facts

In regards to taste and smell, “…water treated with chloramine has less of a “chlorine” taste and smell than water treated with chlorine.”

Drink up!


*“Natural Organic Matter” is defined by the EPA as complex organic compounds that are formed from decomposing plant, animal and microbial material in soil and water. They can react with disinfectants to form disinfection by products. See page 8, footnote #3 of the EPA’s Chloramines Q&A’s.



Featured image was made by the author using PowerPoint

Transporter gif from tumblr


DrRubidium is an analytical chemist that spends her days finding needles in needlestacks. Also a science communicator, she focuses on the the science behind everyday stuff and pop culture.

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  1. Dr Rb, you missed the fact that ALL CAPS EMAILS are even more effective at killing bacteria than prayer, wishful thinking and a 30C dilution of Yersinia pestis combined!

    Thanks for the very accessible explanation. There is tons of nerdy info if you want more and follow the links. I did find one disturbing point in the EPA FAQ on page 21:

    ” Trichloramine may form more easily in swimming pools because of higher levels of chlorine as well as ammonia from bodily fluids that are often found in swimming pools.”

    Blue water, anyone?

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