Jesus says, "Whoever gives even a cup of cold water to one of these little ones in the name of a disciple—truly I tell you, none of these will lose their reward.” (Matthew 10:42)
To us it sounds like such a little thing - but in Jesus' time, cold water was not so easy to come by. There was no refrigeration. Most drinking water was fetched from the well early in the day and sat in a clay jar. It was drunk lukewarm or even warm.
For a thirsty person to receive cold water, someone had to make a special trip to the well. Cold water represented gracious, demanding effort on the part of the giver.
In our acts of hospitality, it's very often the little extras that most memorably convey the love of Christ.