There is chlorine and chloramine which water authorities use. Chlorine can dissipate with boiling or leaving exposed for a period of time before using (like overnight) or by filtering. Chloramine is harder to get rid of. SMB or campden tablets will do it as will ascorbic acid (vitamin C). I use ascorbic acid (from chemist warehouse) at the rate of 0.3g/30L of water,
That will work, its not quite enough if the free Cl is right up at the limit of Australian Drinking Water Guidelines (5ppm). That's only likely to happen if you were very close to the water treatment plant, or there is some sort of emergency treatment (remember giardia) the Cl is used up as it works its way through the system.
Leaving in a bucket can be a lot slower than people think, probably several days in the sun would do it, less I'm not so sure.
If you way overdose, especially with Lager yeast (different way of handling Sulphur than Ale yeast), the extra free S can impact flavours and aroma, if you add early (I'm another brewer that does his water chemistry early - at ambient) then checks the pH at mashing temps. By the time you heat to strike temperature, it will have reacted and most of any excess will have evaporated.
Kadmium and I have slightly different views on K and Na Metabisulfite (NB not Bisulphate) Its the Met part that reacts with chlorine so both work exactly the same way, its just the residual K or Na that's different, at the doses we are talking about I couldn't tell the difference. If you happen to have three place scales you trust then weighing the powder would be cheaper. But reliable scales like that aren't cheap (about three lifetimes supply of Campden tablets).
If you aren't sure how much difference it makes, fill a bottle with tap water, another with dechlorinated tap water, carbonate (fizz tops are handy) taste them alongside each other. There is a big difference, making mineral water at home is cheap and easy for keggers, dechlorinated and it tastes way better.
Mark