Synonyms for Water Level (same or very similar meaning)
WordNet sense 1 (underground surface below which the ground is wholly saturated with water):
water table, groundwater level
WordNet sense 2 (a line corresponding to the surface of the water when the vessel is afloat on an even keel; often painted on the hull of a ship):
waterline, water line
From the ODE community, based on WordNet
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