Pumpkin does work as a good fiber source. Keep in mind there is a fine line between too much fiber and too little. So increasing in increments is better than giving too much right away. My vet had me start with 1T. with every meal, then day by day if things looked better we'd increase it bit by bit. We had to go up to more than a 1/2c. It worked only a short time for my girl. Psyllium is actually Metamucil, it bulks up stool to get the extra water out. It shouldn't be given with other medications as it hinders their absorption. Psyllium should be taken 1 hour before other meds or two hours after. Also if you give capsules make sure your pooch immediately drinks 8 oz of water. The capsules expand like a sponge and they can suffocate if these expand in the throat and aren't washed down into the stomach.
I'm just outside of Milwaukee too.

But I don't think it's the water. It could be other medical issues. My poor girl has had diarrhea now since October/November. It's gotten worse and worse. We've tried everything, Tylosin powder, pumpkin, psyllium, hypoallergenic foods, grain free, (she was on raw before the diarrhea and did well for 6 years on it), we had her prophylactically dewormed, antibiotics, rectal schmear/culture, CBC, TLi and B12 labs, ultrasound and most recently we just started her on Butesonide (steriod). If this doesn't cure it, my fear is there is something worse going on. Let me know if you have any questions, as I've been through and tried practically everything except for the endoscopy/colonoscopy. Good luck to you, I hope you pup gets relief soon!