Laodicea and the cities of Hierapolis and Colosse (Colossians 4:13) were situated in the Lycus valley about ten kilometres apart from each other. Hierapolis had its hot water springs, which can still be visited today. Colosse had its cold water springs. Laodicea was dependent for its water supply on transport by the famous Roman aqueducts and when the water reached the city, it was lukewarm, especially in the hot summers.
During warm days, hot water and cold water are both very welcome as a beverage, but lukewarm water is not tasty and refreshing. It is even unpleasant. Jesus judges this congregation with contempt: I am about to spit you out of my mouth.
16 So, because you are lukewarm, and neither hot nor cold, I will spit you out of my mouth.