I have a 1l waterbottle that I keep filling throughout the day, helps me keep track of how much I'm drinking and I can sip on it all day whereever I am.
Same as Pink Fluff a 1 litre water bottle by my side I use the Buxton ones from Tesco they're on offer 2 for £1 at the moment and I just replace them when the cap hinge is getting a bit weak, probably be cheaper to invest in a proper sports bottle though