I’ve been using a Bru’n Water for about 9 months, using the water quality figures provided by my local water company. I’ve recently bought a salifert alkalinity test kit, and am hoping to use this for the first time on my next brew. The question I have is for the pH value, should I use the suggested value of 8 (if I don’t know the water pH), or should I use the average pH value of 7.7 that I’ve been using thus far? I don’t have a pH meter to take an actual reading.
If you have been using 7.7 for the last 9 months and don’t have any issues then I would just run with that. The difference between 7.7 and 8 isn’t huge and you shouldn’t have an issue.
If you are really worried about it, split the difference 
I’m not sure that pH even affects the calculation as alkalinity drives the calculations.
Good point, I’ll have a play when I get home.
I brewed this weekend, testing my water first for Alkalinity. The results came as a bit of a surprise, with my bicarbonate value (145) rather higher than the values provided by the water company. Seems that my assumption that the variation was minimal, based on the minimal change in value provided by the water company is down to averaging out, rather than a lack of variation.
I plugged the value into Bru’n Water, and used it to build my water profile anyway, but did notice that it stated that my water report was no unbalanced. Should I be worrying about this?
High alkalinity can throw out bad #'s fyi