1.
plain hot water, boiled water
Water that has been boiled and is served hot for drinking, without tea leaves, herbs, or other additives. Valued in Japanese and Chinese health traditions as a simple, gentle beverage.
Usage
Distinct from お湯, which refers to hot water in general (including for bathing or cooking). 白湯 specifically means hot water intended for drinking, typically after being boiled and cooled slightly. Has become a health trend in recent years.
Writing
白 means "white" or "plain" and 湯 means "hot water." The reading さゆ is irregular (not the standard on'yomi or kun'yomi). The "white" refers to the water being plain and unadulterated.