My 2 year old pug has had vomiting issues that we've tried to tackle from a variety of angles. At his worst he was drinking a bunch of water and throwing up immediately afterwards. We were constantly taking him to the vet, and on the last visit she gave him a pepcid shot, an anti-nausea shot, and a water/electrolite pack under his skin that would keep him hydrated as we had him fast for an evening. For the next week we gave him a vet prescribed bland-diet of rice and cottage cheese. That and hypoallergenic food from then on seems to do the trick.
Maybe he has developed a food allergy? Also, he might be eating too quickly. Is there bile in the throw-up, or is it just the food? Just the food suggests he might be eating too much too fast. If he is immediately throwing water back up, cut the water and food for a bit to give his stomach time to settle.
The best thing you can do for him is get him to the vet so they can test him for stuff, though.
"Hi Katharine, Hektor and I are happy to become your long distance friends, though hard to imagine a wee Pug with a long US ancestry that my lad has so he actually has membership in the Ohio Pug Club. Helena"