If you mean Croatian, you must say: "Želim ispiti čašu vode". or "Želim popiti čašu vode". If you mean Serbian, you must say: "Želim da ispijem čašu vode". or "Želim da popijem čašu vode". As you can see, one of the main differences between Serbian and Croatian is using an infinitive after the first verb in the latter. Besides, in the spoken language the last "i" on the end of the infitive sometimes disappears: "Želim ispiti čašu vode" -> "Želim ispit čašu vode".