Good suggestions from paperman27. Have you clicked on the show/hide icon (Next to the zoom % - it looks like a musical note) this will reveal spaces and carriage returns throughout the document as well as table cells.
I also edit a Handbook from information supplied by others. The first thing I do is select the entire document and then set the text to one font and one point size. Then using format painter (The paint brush icon) I set all headlines to similar (larger) sizes and then bold sections. This gives the document uniformity and doesn`t take too long from scratch.
Could I also suggest that if you are squeezing words into awkward shapes around images you will get the "Rivers of White" I think you describe. Try making the print area bigger or the font size smaller so more words fill each line and therefore the spacing decreases.