Definition of "water-seal" [water-seal]

• A body of water interposed as a bar to the passage or escape of gas. (noun)

The Century Dictionary (Public Domain)

• "The tunnel must dip then come up like the water-seal trap under a kitchen sink."
• "For example, water-seal slabs in latrines reduce the breeding sites for culicine mosquitos, vectors of filariasis; treatment of excrete prior to its disposal can kill the eggs and cysts of many human parasites (Ascaris, Entamoeba, and Schistosoma spp), thus preventing contamination of both ground and water."
• "Fixed-dome plants are regarded as leaktight if the water-seal test shows less than 2% water loss, and the gas-seal test shows less than 5% gas loss."