Like at least a couple other Grass Roots hits, someone else did this first -
in this case the Forum , whose 1967 semi-hit version I much prefer.

Intro:

       F                         Eb/F            F
       v  v  v  v    v  v  v  v    v  v  v  v    v  v  v  v
      -/----------- | -x--x--x--x-- | -/----------- | -/--------X--
                     ^^^^^^^^^^ bass drum                 ^ snare

Verse 1:

      Bb         Eb/F    Bb        Eb/F
       v   v   v   v     v   v   v   v
      -/-----/-/---/--- | -/-----/-/---/---

       Bb    Eb/F  Bb      Eb/F  Bb       Eb/F Bb   Eb/F
      The sky was clear on that windy day
       Bb            Eb/F Bb       Eb/F Bb          Eb/F Bb   Eb/F
      'Til the clear blue sky began to turn to gray
      Eb           /Bb   Eb             /Bb   Eb          /Bb  Eb    /Bb
         The lightning flashed, the thunder roared above
       F       /C  F       /C       F            /C  F
      Then fell a drop of rain to start our love

Chorus:

                            Ebm7                   Ab
      [1: Let the river get wide], the river gets long, now
      [2: And the river gets wide]
                    C#7M                    Bbm
      The water runs deep as our love gets strong now
                         Ebm7                 Ab
      So baby, don't you fight and say you belong now
      1:   Fm7/Bb [hold 2 bars]
      2:   Fm7/Bb [hold 6 bars]
      3-5: Fm7-5/B  Bb
         To me

Verse 2:

      Upon the roof we heard the gentle rain
      With the rhythm of our heartbeats, down it came
      As it hit each drop  our hearts could feel the pain
      No one on earth can stop a drop of rain

[repeat chorus 3X; fade 3rd time]


-- another ace 60's tab from Andrew Rogers