The target level for a swimming pool is 1-3 ppm, and the drinking water target is 3-4 ppm. So why do I feel so chlorinated when I get out of the pool, and why do I bother rinsing my swimsuit in tap water that actually has a higher chlorine level than the pool? Is it a chlorine vs. chloramine issue? My tap water using chloramine, which is the undesirable byproduct in a pool of chlorine + human waste.
I thought I understood this stuff because I used to own a pool and I’ve kept aquariums (both fresh and marine) so I do understand the chemistry basics.
You are looking up values but one is a recommended minimum (for pools), and the other is a maximum value to still be in compliance (for drinking water)
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Target values for drinking water plants are not 3-4 ppm. Typically the maximum allowable chlorine concentration is 4 ppm. Most states require a minimum of 0.2 ppm at the furthest point on the distribution system. This may mean SOME points upstream have values closer to the upper end, but the systems are typically designed to keep that to a bare minimum. Plant operators are also trying to reduce costs, so they don’t want to run it up any higher than they need to stay in compliance and ensure bacteriological samples are negative.
Tap water doesn’t usually have higher chlorine levels than a pool. I guess it is possible if the pool is kept kind of low and your city’s water is kept high. I used to work for the water department in Charlotte, NC and they pumped tap water out of the treatment plants at 2ppm. Most of that gets eaten up in the pipes, so depending on how far someone lives from the treatment plant in that case, the tap water is going to be anywhere between nearly 0 and 2. Other cities might use different amounts, but the EPA maximum for drinking water is 4ppm. I seriously doubt that your tap water is 3-4 ppm unless your city operates at the maximum and you live right next to the treatment plant.
I haven’t maintained a pool in a long time, but public pools can be much higher than 1-3. I think it mostly depends on the state/county regulations. The pool I swim in is usually around 5 ppm. You are right about the chloramines that are generated by chlorine breaking down all the body grime. These are what really cause the “chlorine smell” that you get from a public pool. My parents have a pool in their back yard that doesn’t get as many people swimming in it and it never smells nearly as chlorinated as the public pool, even though their levels are very close.
I believe it’s the chloramines that are higher in the pool versus in your drinking water. That’s what makes the chlorine smell and what irritates swimmers’ lungs and eyes. Also, the maximum contaminant level for drinking water in the US is 4 mg/L, so the actual target should be much less than that. We tried to maintain most sampling points at at least 1 mg/L (ppm) at my last job.
It also has to do with the type of chlorine. IIRC, pools should be testing free available chlorine (FAC) since that is what’s available to disinfect the water. Total chlorine is the sum of FAC and combined chlorine, which is already “used.” The pools may have more combined chlorine than the drinking water system.
I believe it’s the chloramines that are higher in the pool versus in your drinking water. That’s what makes the chlorine smell and what irritates swimmers’ lungs and eyes. Also, the maximum contaminant level for drinking water in the US is 4 mg/L, so the actual target should be much less than that. We tried to maintain most sampling points at at least 1 mg/L (ppm) at my last job.
It also has to do with the type of chlorine. IIRC, pools should be testing free available chlorine (FAC) since that is what’s available to disinfect the water. Total chlorine is the sum of FAC and combined chlorine, which is already “used.” The pools may have more combined chlorine than the drinking water system.
My system (in Northern Virginia) definitely uses chloramine. (Once a year for a couple weeks they switch to normal chlorine for some reason, and I can smell and taste the difference.) Isn’t “using” the chlorine the same as creating chloramine?
I think the chloramine in the tap water loses much of the chlorine along the way. My water tests high for ammonia and nitrite straight from the tap, which has caused problems keeping sensitive fish in the aquarium.
My system (in Northern Virginia) definitely uses chloramine. (Once a year for a couple weeks they switch to normal chlorine for some reason, and I can smell and taste the difference.) Isn’t “using” the chlorine the same as creating chloramine?
I think the chloramine in the tap water loses much of the chlorine along the way. My water tests high for ammonia and nitrite straight from the tap, which has caused problems keeping sensitive fish in the aquarium.
Yes, you are right about “using” chlorine being the same as creating chloramine (also known as combined chlorine). I read somewhere that the reason for using chloramines to disinfect drinking water is the recent disinfection byproducts rule. Chlorine produces more byproducts than chloramine, and when the EPA started the DBPR, systems started using more chloramine so they could reduce the disinfection byproducts (trihalomethanes and haloacetic acids). I think it also persists longer in the system, which means if you’re far away from the distribution system you don’t have to worry as much about getting low chlorine residual.
Your ammonia and nitrite comment made me curious, so I looked it up. Apparently the reason the distribution system switches to chlorine periodically is to get rid of the ammonia and nitrite. The ammonia is there because chloramination is just adding ammonia and chlorine and inducing the creation of chloramines, so they may not have balanced that mixture adequately. Biofilms can build up in the pipes, especially at the ends of lines and lower demand areas, and the bacteria in those biofilms convert the free ammonia into nitrite. Apparently the chlorine disinfection starves those bacteria and ends the nitrification process. I just learned something new, so thanks!