N.H.
Hi M.,
18 months may be a little early to get rid of the bottle and onto a big kid cup right away. Find a good sippy cup first. I found ones that my little one likes from Walmart, I think it is a NUBI? They were cheap, they dont leak.
At around 12 months, I started with sippy cups for my little one, and at almost 3, she still uses one for nap and night time. She gets one with milk, with a splash of flavored coffee creamer for taste (she doesnt like milk alone), warmed just a little, and a water cuppy with her in her crib at night. Other than that, she only gets a big girl cup with juice or milk with meals and snacks. She just recently started with the big cups a couple months ago.
Good luck