My girl don't like to drink plain water

You can also try making it into a "fun" activity. For some reason, my friend's son really loves doing the "yum seng" cheer. So my friend would bring his bottle/cup to her son and get him to do the "yum seng" and bottoms up. hahaha.. He never gets tired of it and always gets "tricked" into drinking his water (he also doesn't like drinking plain water otherwise). Perhaps you can try getting your girl to pick up a special mug to encourage her to drink more water? If not, adding some flavours by diluting juices or adding fruits (like what Vanessa) suggested may work as well. :)