There's nothing wrong with providing a large water bowl for them to soak in. They have access to water in their natural habitat. VPI's care sheet claims that they 'hide' in water when they feel insecure. My only response to that is that, well, there's nothing stopping you from adding a hide or two big enough for your macklot. Big hides for bigger snakes can also double as perch areas and basking spots. In addition, replacing a big water dish with a small water dish doesn't remove any 'insecurities' they snake may have.
I don't keep this species so beyond that I can't give much advice.