Go here to download the spreadsheet:
Version 1.7 (2-26-10)
Step 1: Enter your starting water profile, mash & sparge volumes, and dilution rate (if any).
Step 2: Examine the results.
1) Residual Alkalinity (RA) - See if the corresponding color range (SRM) matches the beer you are brewing. If not, the RA will need to be adjusted in order for the mash to be at the proper pH. Step 3: Modify the results by making salt additions.
2) Chloride to Sulfate Ratio - Determine if this needs to be adjusted in order to match the style/flavor of your beer.
3) Individual Mineral Levels - Take note of which mineral levels need to be adjusted in order to fall within the recommended ranges shown. Alternatively you can try to match these levels to a particular region or other set of guidelines.
The goal here is to get: 1) The RA to coincide with your recipe color, 2) The chloride to sulfate ratio to a desired flavored profile, and 3) The individual mineral levels to within recommended ranges. Notes:
Add mash salts directly to the mash. Add sparge salts directly to the boil (not the sparge). You may choose not to add certain salts to the sparge water in order to keep some minerals lower in the total water (sodium for example). In this case, simply uncheck the appropriate box.
For an excellent video series about adjusting water using this spreadsheet (courtesy Bobby M), go here: Water Modification Videos, TH's Spreadsheet
For more information about how this works and why, I highly recommend reading John Palmer's entire chapter on water found here: http://www.howtobrew.com/section3/chapter15.html
Source: The recommended mineral ranges, RA to SRM recommendations, and Cl to SO4 ratio recommendations are all based on John Palmer's RA spreadsheet and pH nomograph.