Try those little juice boxes...they make them for babies/toddlers and hold the straw to his mouth and squeeze a bit in at a time. This is how I taught my DS to drink from a straw. He now holds it (well snatches it off me ) and drinks independently. He thinks he is a clever little thing...then you could try a cup with a straw or a bottle of water with a straw.

Have you tried those pop top bottles. Fill one with water and let him try, most babies love them!!