I taught Ben how to drink from a straw. At first, he didn't know what was going on. He kept chewing at the straw. Then, he even blowed into it. But after a lot of exaggerated gesticulations on my part (think Mommy puckering her lips like a sucker fish), he finally got it, about 2 weeks ago! Since then, it's become like a game. Let's see how much water I can get in my mouth with this strange thang. suck suck suck suck suck cough suck suck cough.
It's great, especially since Ben is eating quite a lot of "solid"-y type foods now - thick porridge, mashed (not pureed) carrot & sweet potato, mashed baked beans, etc. - so more hydration is important.