Emphatically no. You cannot discharge urine into the cut under any circumstances!
Our position has always been that it is not only undesirable, but is actually illegal to discharge urine directly into the canal. The same rule applies to many rivers, and we expect that any waterways not currently covered, soon will be.
Why? Urine is generally sterile§ when it leaves the body of a healthy person, however it contains a lot of nitrogen, which acts as food and can promote the excessive growth of undesirable algae in the canal or river. This can lead to serious consequences for anyone who comes into contact with the water, and can ultimately lead to loss of aquatic life too.
It’s simply not fair on the environment and other canal users to discharge urine into the cut.
If you have a compost toilet on your boat, the responsible thing to do is to have a method of collecting urine and to empty it down a land-based toilet, elsan point, or into the ground away from the cut, ideally changing the discharge place regularly.
Unfortunately, some compost toilet resellers have been giving out incorrect information and boaters are now facing fines and having to retrospectively look at fitting a method of collecting and correctly discharging urine.
§ If you are on any form of medication, particularly anti-depressants and chemotherapy, your urine will contain traces of these substances, which can create issues for the aquatic life of the canal. Discharging to the ground enables naturally occurring bacteria etc to attack and break down the traces of medication in most cases.