Water is a vital part of your success, so in order to increase your performance you must hit your daily goals. It is recommended that you drink half of your bodyweight in fluid ounces. So contrary to your gym friends general advice, this also means that everyones daily goal is different. If you aren't sure are how to do the conversions yourself, there are tons of resources on the internet. The link below is useful in doing the calculations for you so that you can be properly hydrated which will improve your health and performance.
Enjoy your improved health via nature.
Stay healthy my friends,