Much water goeth by the mill
That the miller knoweth not of.

John Heywood (1497?-1580?) English playwright and epigrammist

Proverbes, Part 2, ch. 5 (1546)
    (Source)

See Shakespeare, Titus Andronicus, Act 2, sc. 7 (1588-1593): "More water glideth by the mill, / Than wots the miller of."