Thats very interesting that the coughs have lessened. It's the same thing that happened here at first.
(I just reread your post and saw the coughing started when some of the unfiltered water was used instead.)( I guess my next 3 questions don't apply now.)
What was happening before 3 months ago when the coughs started?
Did you just move to a home with chlorine or did the water company start putting it into the water supply? (The latter is what happened to us).
Did they just start drinking tap water? Maybe they used to have only box juice or milk?
Call your water company and ask if they just started putting chlorine into the water supply. Thats what happened to us.
It went like this. The coughing was gone as soon as the first 24-48 hours had passed after stopping chlorine water drinking. Since we were still living at the home with chlorine a morning after a bath was still effecting our much smaller child who had been more ill with the cough the whole ten months. The morning after an evening bath she would have a mild cough. This patteren showed up because she did not get a bath every night. The coughing stopped completely after we moved in to our bran new home with its own well. And of course no chloriene.
Even tho they have never had coughing associated with pools with chlorine water, I attribute this continued coughing to the bathroom being so small ,warm water, and not ventilated well at all and likely because of her age playing and probably drinking some of the water while bathing was very likely.
The pediaticians my kids have seen for the last 16 years have never heard of this allergy/sensitivity. I'm not even sure if they ever believed me. I told them every thing that has happened when the chlorine thing first happened 9 years ago.
I've also researched this in Medical books at our local library and discovered testing that had been done on humans being in contact with chlorine and the symptoms the tests showed were the same symptoms as my kids had.
I believe there may be many people out there just always getting medicines forever from doctors who a lot of the time can only treat the symptoms and its up to us to figure out whats really is going on.
Keep in touch.
I'd be really interested if the kids baths are given every night.