The Spanish lavar (“to wash”) comes from the almost-identical Latin, lavare.
From the same Latin root, we get the English… deluge. What is a deluge of, well, anything if not a flood of it?
Of course, this also means that the English antediluvian (literally, “before the flood”!) also comes from the same root!
We can see the parallel more clearly if we note that the l-v root of the Spanish lavar maps to the (d)-l-u of deluge, with the -u- turning into its cousin -u- during the process.