Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you today. I do apologize that your question was not answered before. Different experts come online at various times; I just came online and wanted to touch base with you.
Hopefully Moonpie is still doing OK and that this was a very dilute dose he had. The problem with bleach is it will damage the throat and stomach. If you have not already you could give him milk to try to dilute it more and coat the stomach. Else the key is close monitoring (do no induce vomiting as it could do more damage on the way up) and supportive care. Any vomiting, belly pain, paling of the gums (going white) and we'd want him seen by a local vet urgently.
As you monitor, you can go easy on his stomach with a light diet (eg cooked white rice with cottage cheese, scrambled eggs, boiled chicken, boiled white fish, or meat baby food (as long as its garlic/onion free)). If he seems nauseous, you can give an OTC pet safe antacid [ie Omeprazole (0.25-0.5 mg per pound once daily), Esomeprazole (0.25-0.75 mg per pound once daily)]. But as this was a small dose and in water, hopefully the overall amount of bleach he had was small and not likely to cause severe damage.
Finally, just to note in case you were keen to have your wee one seen today, some vets in our country have office hours today. As well, I wanted to mention that most practices have contingency plans for emergency care for their patients even when they are closed. Therefore, it is worth ringing the practice. If they are open, you can get in today. If they aren't, then they will likely have a message to direct you on contacting their out of hours service. And if you don't have a vet, you can find a local one via the RCVS Register (http://findavet.rcvs.org.uk/find-a-vet/) or Vets Now (http://www.vets-now.com/find-an-emergency-vet/) who are open all nights/weekends. In any case, if you wanted to get this checked out sooner then there are options to do so.
Kind regards, *****