To Buy:
Best thing is - it's free! Bottled water can be bought from supermarkets and most stores nowadays.
To Store:
Store in the fridge to keep chilled, though the body digests room temperature water much more easily.
Tips & Tricks:
To ensure you take in two litres daily, have a glass of water as soon as you wake, and another before breakfast. Another mid-morning, before lunch and a couple in the afternoon. One more before dinner and another prior to bed, and you've completed the requirement without any extra hassle.
Cooking Tips:
Replace some of the oil used in recipes for stir frying with a little water or stock to lessen the fat content.