Make free drinking water available by way of water fountains/stations, especially after security checks.
Why is this important?
Clean drinking water is a basic human right. Plastic bottles are polluting the oceans. People would bring their own drinking water in their own re-usable containers if they were allowed, - but they are not.
Apart from generating polluting plastics, airport shops charge for water at often 5 or 6 times the price it would be in a supermarket.