Chances are you are not going to find any rule about this.
Personally, I would say that a vampire digestive system no longer functions normally, so eating is going to be a problem. Not to sound to gross, but you can probably get away with chewing and swallowing, but it will have to come back up the same way. Drinking should not be a problem as vampire’s drink blood. The vampire would not get any benefit from drinking anything.
You could probably disguise breathing, eating, or sleeping with, well, a Disguise skill check. Or possibly Bluff? I don't know how many people actually pay attention to such things, since there are plenty of ways for the living to avoid needing to breathe, eat, or sleep... pretty sure there is an Ioun Stone for each of those, actually.
For hiding other aspects of being a Vampire... Penumbra Tattoos should help you from roasting in sunlight. Angelskin armor should help hide the "evil" associated with being Undead. Picking up all four of the Damnation feats can definitely help hide one's alignment, as well. If you happen to have a swim speed before you are turned, then you don't have the weakness to running water.
The real question is how are you not a mindless spawn being controlled by the Vampire that turned you? Very few abilities protect you in a way that allows you to keep your free will upon turning Undead, especially by an Undead with Create Spawn. Such an ability is the capstone for the Agent of the Grave prestige class, as an example of how rare that really is.
Remember in Dracula/Nosferatu when the vampire was entertaining this guest who was a journalist who asked absolutely no questions about why he was the only one eating at the vampire's dinner table? Should be easy to hide against anyone who has no ranks in Kn Religion. However, against them, the biggest thing would be hiding things like never going out in the sun.
Re: Not being a spawn/under control, the creating creature can just choose to release you immediately upon creating you. Technically, being a spawn doesn't even refer to being under control however, it basically just means "newly minted, weaker, fledgling" vampire that may not even be able to use or properly control all it's powers. A vampire spawn at least cannot figure out how to grant the unlife to other vampires, and usually cannot control its cravings, hence they are usually considered feral and untamed by other vampires.
Get a Ring of Sustenance. Then you never have to explain it to anyone.
Get a Ring of Sustenance. Then you never have to explain it to anyone.
if you lack founds, get a pair of gloves and claim you have a ring of sustenance under it. (and refuse to remove the gloves, you wear them to prevent the expensive ring from being 'stolen')
also remember vampire are :
Shadowless (Ex): A vampire casts no shadows and shows no reflection in a mirror.
- so avoid mirrors and brightly lit rooms.
also in the speed section it say that vampire with swim speed does not take 1/3 of their hp as damage from running water, so get a way to gain swim speed asap.
-side question:
what is considered 'immersion in running water'? is a decenter of endless water going full force at a vamprie deal that 1/3 damage as well? (if he's immersed).
lastly, always knock on doors, you'd be surprised how many would yell 'come in'.
(Vampires cannot enter a private home or dwelling unless invited in by someone with the authority to do so.)
Immersion usually means almost or fully submerged, not just sticking your feet into a shallow brook, but intentionally wading into a deep ford or being thrown into the water while bound like one would a witch to see if she is made of wood.