The wee little bit of chlorine in municipal water supplies isn't gonna hurt anything. Yer filling the res outta the ymca swimming pool, differant story. But basically, if you can shower in it without going blind, it won't hurt yer plants.

You're not talking about thiosulfate drops, are you? Like aquarium dechlorinator? Those work by binding the chlorine to sodium- = NaCl= table salt.

I'll go w/ 15-50 ppm Cl, myself.