If I have a bottle of water by my bed, do I have to say the blessing every time that I take a sip, or is one time enough.

Thanks for your question, One time is enough. However if you take more than a half an hour break between sips then better to make a Bore nefashot on the last drink and then say shehakol again on the next drink. (See peninei halacha brachot chapter 10, halacha 13) All the best!