Does the water tank HAVE to be in the shed? Can it be outside the shed?
doesn't necessary have to be in the shed but it would have to be covered else it would go green from the sunlight, also what would you do in winter when stuff freezes?
Get your tds done and then worry about the rest after..
you havent said how much water you need a day, what vehicle you will use, are you going to wfp the whole house or just upstairs? If you just ask "what do i need" your going to get lots of people throwing stuff at you which will end up confusing you even more. You can have something as small as a 15lt backpack and barrels or a full blown 1000lt crash tested hot water machine and everything inbetween.
Give as much information as possible mate its easier to steer you in the right direction then.