Watch the The Water is Wide online guitar lesson by Stephen Bennett from Harp Guitar Basics
I would encourage you to fool around with the interval of a tenth that I talk about on the video. Remember - it's just a third PLUS an octave. Whenever I get the chance to have one of the sub-bass strings ringing with a harmonic on another string creating that interval - I go for it. With gusto! Because - it sounds beautiful and full and while it's ringing I can play a melody on different strings - which all together, creates a wonderful sound.