In Exodus 15:8, this signifies falsities gathered together. Waters normally signify truths, but in this case, where they were blocking the escape of the Children of Israel from slavery and signify the opposite: falsities.

(References: Arcana Coelestia 8286)

'Three' denotes fullness, and 'a third,' not full.

(References: Arcana Coelestia 2788 [1-13])