Top off water question

6 or 7 years ago when I got my start brewing I read somewhere (must of been Dave millers home brewing book) that the night before you brew fill a large pot with around 3 gal of water and boil uncovered for 20 min to have clean chlorine free water to top off your fermenter with. A couple weeks ago I read in a forum where one guy just fills up a pot and let’s it sit uncovered all night and the chlorine will evaporate out. If it I’d a good practice that would be a better route for me as it uses a lot less energy. My question is what does everyone on here do for their top off water?

The fastest and easiest thing is to treat it with campden tabs. They’re dirt cheap and 1 tab will treat 20 gal. instantly. Another advantage is that the remove chloramine also, which neither boiling or letting it sit will do.

I do extract and partial mash brewing and usually end up with about 3 gallons of wort in the 5 Gal. BK. For top off water, I buy a 2.5 gallon container of distilled (or spring water if distilled isn’t available) from the grocery store for about $2.50. On brew day I put it in the chest freezer (or outside when it’s cold) a few hours before I need it. Since it’s already pretty cold, I spend less time chilling the wort down to pitching temp and only need to get it down to 100* or so.

It has a built in spigot that I spray some Star-san on a couple minutes before using. I add about 1-1.5 gallons to the fermenter and pour the wort over it through a sanitized strainer which strains out any non-liquids, partially mixes it with the water and provides some of the aeration needed. I top off up to 5.25-5.5 gallons with the remaining water from the container, put the lid on and shake the bejeezus out of the bucket. At this point, I’m pitching in the low 60’s.