You can lose some weight by just drinking water and not eating which is also known as fasting but it's not a really healthy way of losing weight.
If you want to fast for a few days and only drink water and not eat then that's okay but you do need food to stay healthy and have energy.
So just eat foods low in calories such as salads, soups, tomato soup, potato soup etc and you should still lose weight while fasting every few days.
Exercise also helps you lose weight so get out and jog or walk even 15 minutes per day or ride a bicycle which can help you shed the pounds.
Drinking some Apple Cider Vinegar also helps with weight loss too.