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:

       F5                         Eb5            F5
       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:

      Bb5         Eb5    Bb5        Eb5
       v   v   v   v     v   v   v   v
      -/-----/-/---/--- | -/-----/-/---/---

       Bb5    Eb5  Bb5      Eb5  Bb5       Eb5 Bb5   Eb5
      The sky was clear on that windy day
       Bb5            Eb5 Bb5       Eb5 Bb5          Eb5 Bb5   Eb5
      'Til the clear blue sky began to turn to gray
      Eb5           /Bb5   Eb5             /Bb5   Eb5          /Bb5  Eb5    /Bb5
         The lightning flashed, the thunder roared above
       F5       /C5  F5       /C5       F5            /C5  F5
      Then fell a drop of rain to start our love

Chorus:

                            Eb5                   Ab5
      [1: Let the river get wide], the river gets long, now
      [2: And the river gets wide]
                    C#5                    Bb5
      The water runs deep as our love gets strong now
                         Eb5                 Ab5
      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: F5  Bb5
         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