This sounds horrid I know but can you catch it in a container and keep it? Seriously - and don't worry about the pee, a lab has always seen worse.
Could this have been a nemotode worm? I think if anything had been in your bladder / urinary tract that shouldn't be there, you would have felt at least some unusual sensations if not pain. So if it is a nematode, and big enough to see, it is more likely to have come into your water system than from your body. Having said that different species are parasitical to humans but are usually v tiny.
This is why you need the creature to be identified. If it has got into your water supply this implies some kind of pollution and your water supply company may need to take action - or your own house system may need investigation eg has a pigeon sh@t in your header tank etc
Local environmental health dept at the council might be a good first start.
From experience, I would suggest if you rely on your water company alone they will see this purely in terms of hushing up bad publicity and so you need a neutral body such as the council to help you out.