i see that you are interested in the shoulder sling bag.
this bag has served me well in many different incarnations, both store bought and homemade. it is a good bag for carrying small loads, such as on a jaunt about the back yard woods hunting for walking stick saplings or taking short day hikes. i might even consider it for an overnight bag, providing the strap has a good weight distribution property.
but, when it comes to carrying water, a small camelback sized backpack really comes in handy. this carries all that the shoulder bag will, but it will put the gear much closer into your body and keep it much more secure. this has good and bad results, depending on your use. if you need to get into your bag alot, it can be a pain to pull the back off your back constantly, versus swinging the satchel around to the front and flipping open the flap.
for me, water is about the heaviest thing i carry. for me, one liter of water often weights about the same as the entire rest of my gear. i guess you coudl say i travel light. either way, i don't like a heavy solid water bottle flapping against my hip as i travel.
i pretty much go back and forth between shoulder sling bag and a small light backpack, it really depends on my mood. also, a backpack is easier to lash a hatchet or large knife to, if that is your prefered carry option.