Though you don't necessarily have to fully clean your CamelBak every day, it is recommended that you at least clean it with soap or other cleaning agents once per month. However, you should still empty your CamelBak and leave it to dry every time you use it to avoid bacterial or mildew buildup. Note that there isn't anything wrong with using soap on it every time, it just isn't necessary if you're only putting water in your CamelBak.