The majority of drivers said they had "many times" or "sometimes" had to urinate by the side of a road or behind a tree while on bus-driving duty and nearly all drivers surveyed had restricted their water intake.
"Drivers have been minimising their water intake to avoid the need for urination, risking dehydration, possibly leading to kidney damage, headaches, and concentration issues," Savell said.
Public urination also opened drivers to criminal prosecution.
Both councils were provided with the survey results, but the union felt there had been no improvement since and decided to make the information public.
Union members have agreed that from March, when they need to use a toilet, they will stop outside the Dunedin bus depot, offload any passengers, then drive their empty buses into the depot, park, and use the toilet facilities provided there.
They would then pick the passengers back up and resume their journey.
If the driver's route did not pass the depot, the driver would take the shortest diversion to the depot.
Savell said another major issue — which could also see changes to where union members stopped if not resolved — was that many stops were too small for buses to drive in and out of, meaning the bus had to block the road outside the stop.
An example was a stop on Macandrew Road, near the intersection with Wesley Street.
It is one of several on the street the city council is to consider approving changes to, following a proposal by the regional council.
The stop is 14m long, the length of a bus with a bike rack down, and cars often park close to the yellow lines on either side of the stop, causing stress for drivers, and sometimes resulting in parked cars being clipped or bus drivers being abused by other road users for blocking the road.
It was also an issue for passengers with limited mobility, who often could not get on to the bus as it could not get close enough to the kerb.
Savell said it would be good if the council would fix the problem at the Wesley St stop.
There were about nine other stops with similar issues.
If they were not fixed, union members would, from March, boycott any new or upgraded bus stops that did not meet requirements.
Regional council transport manager Garry Maloney said it was aware of the concerns raised by the union and had been working on understanding the details.
The council would discuss working together to find a solution with those involved in delivering the bus services.
