Join ASPE and they send you a data book every year (or equivalent on CD).

You can order the Plumbing Engineering & Design Handbook of Tables, which is a ~4" thick book of about every table/formula/equation you could want.

Or you can search on the internet (trial and error) and find a lot of information that way - some are even in pdf form.

My "personal design handbook" is not in electronic form, and frankly I would not want it that way. I like the feel of paper and being able to write notes as needed. Also, adding/removing information is so much easier when it is in a 3-ring binder.

As for the contents of my book; it consists of select sizing table and charts from building code, white papers on various topics from Sovent systems to gas systems to compressed air systems. One section I have is pages from an old A.O. Smith catalog on sizing/selecting water heaters for various applications; also in these pages are schematics for using multiple water heaters.

That plus a handful of Excel Spreadsheets I've got informaiton for most anything I need. Is it comprehensive with informaiton for any plumbing system? No, I would need 2 or three binders for that. And with that, I recommend building your own handbook with informtion that's most relevant to what you are working on.