lemon water
Plain water with lemon juice or slices, typically unsweetened.
朝起きたら、まずレモン水を飲むようにしている。
I make it a habit to drink lemon water first thing in the morning.
Sweetened lemon drink; often used interchangeably with レモネード, though レモン水 can also refer to homemade or less sweet versions.
See also: レモネード
暑い日には冷たいレモン水が最高だ。
On a hot day, cold lemonade is the best.