Using water straight from tap to top off fermenter.

if you are satisfied with your beer then there is your answer.
tap water has a lot of advantages for a brewer. its cheap, available and usually excellent quality.
removal of chlorine (easy) and/or chloramine (more difficult) is typical. remember too that most all brewers in this country obtain water right from the municipal supply.
lastly, adding water to fermented beer can also add oxygen. boil and cool if your beer has fermented.
Cheers.

 

I used to do it all the time, before I started treating my tap water with Campden tablets to remove chlorine/chloramines. Never had an infection due to this (AFAIK).

 

There may be more homebrewers drawing their water from municipal sources than those on well-water but 'most all' seems a bit overstated.

Does this stat come from AHA?

 

I use to boil every drop of water before using it, now days I add tap water directly to the fermenter (NYC water) every one is happy, me , my beer and the yeast

 

by brewers I mean breweries, not homebrewers. not sure how many of us are treating their water. probably a lot more than 10 or 20 years ago.
Cheers.

 

For about three batches, I topped off (I was using bottled spring water back then tho). Then I started doing full boils, even for extract, by using more than one boil pot. Haven't topped off since.

It's doubtful that there would be any issuew with topping off with tap water tho, unless your water is just lousy tasting (think socal, at least some parts of it) or if you have significant chloramine content. Many, many municipalities use at least some chloramine*, often in differing amounts by season (or whatever other parameters they use for such decisions). I am not certain about the use of chloramine where I'm at now, so I add about one campden per 4-5 gallons of water. The water comes from a water company, so it's likely treated, and thus will have a fairly high probability of having chloramines. I'm playing the odds, and playing it safe, and it's working just fine. Other than a presumed degree of hardness from limestone (Edwards Aquifer), it's actually very high quality water, and has made lots of tasty batches of beer so far.

*Source: a professor at the college who teaches classes on water treatment and related topics. For your local info, check your water report, write the water company, or have your water tested. Or just add campden, just in case, like I do. I have noticed no ill effect on beer flavor from the campden. I have however, noticed effects from chloramine, way back when I actually used my mr beer keg to make mr beer kit beers. Water heavy with chloramine will make beer that tastes like band-aids. Back then, I didn't know about campden, so I solved the problem by using bottled spring water.

 

Tap water is sanitized, so it's safe to use as top-off water as-is, as long as it tastes good. There's no need to boil it. Regarding chlorine/chloramines, as i understand it (and I could be wrong), the ill-effects are primarily mash-related. Using it to top off your partial boil shouldn't cause any problems.

FWIW, Chicago - a fairly good sized municipal water supplier (a good chunk of northeast Illinois) - does not use chloramines. thus, a simple charcoal filter is all that is necessary to remove the chlorine, if you're so inclined. I can't speak for other big municipal suppliers, but I thought this might be relevant, albeit tangentially so.

 

I'll go out on a limb and believe you here. I think it need be said that a quarter of a crushed campden tablet is about a penny or 2 cents. It takes 10 seconds. It's insurance and it's totally worth it.