Use 'tepid' to describe something warmer than cold but not hot, like a bath. After adding some cold water, the bath became tepid.
Pro Tip 2/3
Negative Implication
'Tepid' often suggests disappointment, as when something is expected to be hot. I was looking forward to a steamy shower, but it was only tepid.
Pro Tip 3/3
Subtle Warning
Describing food or drinks as 'tepid' can hint they are not fresh or properly prepared. The soup arrived tepid, hinting it had been sitting out too long.