My dog has had her booster recently but has stopped eating but is drinking loads of water?

How long ago was the shot and when did he stop eating? How old is the dog and what kind? Did you call the vet?

There are side effects to some vaccines, some ar emore common than others, it's time to make a call to the vet to let them know what's up.

I agree it's time to let your vet know what's up. If by booster you mean vaccine then you could also be seeing a little sluggishness as a side effect. I would also like to think that your pet had a physical exam before the booster was given.
Could be that he is reacting to the injection, but could be that there is something else going on.
Joy makes a good point about age, older dogs can start having health issues that will make them drink more.
What is his age?

Diabetes and kidney damage can cause excessive water intake and loss of appetite. Neither shows up on a pre vaccine exam (the normal kind) without some blood test or mention of a problem by the owner.

Granted,more should probably be done on the 'annual' exam and vaccination, but that would drive many people away because of the costs. New vaccine protocol will probably do away with the annual visit and 'exam', anyway.

Nothing beneficial causes this abrupt change in water intake and eating... best get the vet in on solving the problem, ASAP.

Maybe a blockage. Just because your dog just got its shots, doesn't mean that it didn't eat something it shouldn't have ;)

Either way. I'd call the vet...