Re: Bru'n Water - mash and sparge water Total Water Additions
The water quality needs of mashing and sparging water can be quite different. If you were brewing a light lager, then maybe the water qualities would be similar. But for many other styles, the water qualities can be different (its just the alkalinity that differs). Therefore, treating all water used in brewing to some fixed alkalinity level is not appropriate.
In general, all sparging water should have low alkalinity. I expect that the Murphy's recommendations do provide that. However since some mash grists can be more acidic than others, a little more alkalinity MIGHT be desirable in the mashing water to help avoid an overly low mash pH. So brewers should treat their mashing and sparging waters slightly differently depending on the needs of the mash. If a brewer has an alkaline tap water, they may not need to acidify the mashing water to the same degree as the sparging water for all brews.
Murphy's recommendations for acidification are safe since having low pH is better than having high pH in brewing, but that might not produce the best beer. Given that the ionic profile of the brewing water should differ between some beer styles, giving a blanket recommendation for brewing water adjustment is not really feasible or appropriate. Before the application of tools like Bru'n Water, it wasn't really feasible to know how much to vary your water treatments. Now water treatment is more practical to the layman.