Thank you Natalie,
I must say that I am a wee bit concerned about Colin (especially if he is now uncomfortable and groaning do to the distension causing him discomfort).
When we see excessive drinking, it is often an ongoing signs associated with health issues (ie diabetes, Cushing's disease, or organ dysfunction (ie liver, kidneys)). Still in Colin's case where we are seeing excessive drinking as a short term sign (perhaps a one off), we have to consider this is a sign telling us that he has some GI upset and/or GI distress (just as they will eat grass to make themselves vomit) and a specific sign of disease.
Now GI upset/distress can arise for a range of reasons. If Colin has overeaten this morning, eaten something he should not have (that is becoming stuck) or has an ongoing health issue (ie infection, inflammation, etc). And we have to appreciate that if Colin has just had a breakfast of kibble and has than added a large volume of water to that kibble in his stomach, he will cause the kibble to expand. Together (expanded kibble and water) can cause stomach distension. This is often uncomfortable, could cause groaning/discomfort and is likely what you are seeing just behind the ribs. If the food/water overindulgence were the only issue, than often resting the stomach by withholding food/water for a few hours and treating with a GI lubricating treatment (ie Lactulose from the chemist, cat hairball treatments, etc) can help them get over this.
That said, where my concern for Colin lies is that you feel he is bloated beyond the rib cage and through the whole GI. This tells us that there is something more going on. And since he is a fairly young dog, I'd be concerned if it is possible that he may have ingested something that could have gotten stuck (or something toxic that could harm the GI). Any feces in front of an obstruction could still pass but his kibble would not. Furthermore, we can see distension appear as gas accumulates. Often dogs with GI obstructions are restless, have belly discomfort, may groan or vocalize, can appear distended, may start to vomit or have diarrhea (which can have blood or be discolored). And this would be a concern for Colin.
As well, though usually not related to the sudden onset of excessive thirst, we can see growths or fluid build up (related to heart disease, infection, liver troubles, cancer, etc) cause this type of distension. But with his lack of fitting history, these would be considerations though perhaps less likely.
Overall, Colin is not giving you a straight forward signs of what is amiss for him. The signs alone that he is showing we may be facing a benign issue that would pass by resting his stomach. Still if he is truly looking distended all the way down to his genitals, we do have to be concerned that there is something more serious afoot. Therefore, since it is the weekend, I would strongly advise having him checked today (to avoid any ER visits later). The vet can feel his belly and if he just has an overfilled stomach than they can dispense lactulose. But if there is swelling lower, then the vet can assess this and just make sure there is nothing sinister here like a trapped foreign body in his Colin's GI. So, in this case with his unclear presentation and groaning (a sign this is uncomfortable for him), it would best to have him seen today to just make sure Colin hasn't done himself any harm.
Finally, just to note in case you were keen to have him seen today, some veterinary practices in our country have Saturday office hours. As well, I wanted to mention that most veterinary practices here do have contingency plans for emergency care for their patients even when they are not open. Therefore, it is worth ringing the practice. If they are open, you can get him seen today. If they aren't, then they will likely have a message to direct you on how to contact their out of hours service. And if you don't have a vet you can find one local to you, you can check you can check the RCVS Register (HERE) to find your local Vets Now (LINK) who are open all nights/weekends. In any case, if you wanted to get him checked out sooner then there are options to have him seen today too.
I hope this information is helpful.
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All the best,
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