Is a employer/contractor required to provide potable water to employees that service client locations?

I'm an electrical apprentice and at every job site contractors have provided water. There's typically 4 - 10 employees at the site. Recently I went on a job site with a foreman and they told me the contractor did not need to provide water because we were doing a service job and it was just the two of us. There was no potable water available. Therefore I would be required to carry my own water in those situations. I've looked and found nothing on situations like this. Are there certain situations when employers do not need to provide water/bathrooms? Such as if we were working a residential job.