My girl also started out not liking to drink water but slowly she learnt to accept it. Have a routine and start out with a little. Even if it's one sip, it's still a good start. Make it a big deal even if it's just one sip (i.e. clap hands). Or you can try sharing a cup with him. Make it look like it's really tasty.
My girl only recently (14 months) learnt to suck from a straw so no worries about it. He will get to it one day.
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