Water is a very important factor to make cps feel good or bad. Tap water is so different concerning hardiness depending on where you are living. Btw aged tap water has some advantage because the contained chlor can escape.
To really come to a conclusion you've to use a conductivity meter.
I mostly used rainwater which has a conductivity of 30 ppm when it is fresh. I collect it in a plastic rainwater barrel. After staying in it for some weeks the conductivity goes up to over 600 ppm. Using this water makes my cps looking unhealthy and some neps stop producing pitchers. After noticing this I used RO water. Bad thing was that my dogs had killed my conductivity meter so I didn't noticed that the filter of the RO machine wasn't working anymore. I guess it dried out. A few nep seedlings died. After getting a new conductivitiy meter I noticed that the "RO" water had a conductivity of over 400 ppm. This water was even worse than the old rainwater though it had a less hardiness than the old rainwater.
Utris reacted different to this hard water. While U. sandersonii had no problems with it U. livida (which had grown before like weed) was about to die.
My plants told me (in the way they are growing, colouring and pitchering) that they like fresh rainwater most. But also this might be depending on where you are living. If there is a sulfur cloud over your house than fresh rainwater might be also bad
