My boxer is 10 years old and has water diarrhea all the time

Hello, you are through to Dr Linda, a UK based vet.
I'm sorry to hear this and appreciate how difficult a situation you are in.
Unfortunately, there is a concern here that he has a serious medical issue, especially given his age and breed.
We would consider intestinal cancer, kidney disease, diabetes etc.
He does need to be seen and to have some tests run so we know what we're dealing with and what the best treatment would be. Your vet will talk you through any estimates and may be able to offer a payment plan or payment via credit.
At home we are limited and I would simply advise ensuring he is up to date with a good quality wormer such as Panacur and he is getting a balanced, complete adult food. We can also start a probiotic anti diarrhoea paste such as protexin prokolin, which may help.

this is the only way we can determine why he had these signs and what can be done.
Hopefully we can get to the bottom of things soon.

Not at all. Please feel free to keep me updated and to ask any further questions you may have. Wishing Doc all the best.