Russian Tortoises & Drinking Water Question

I have been keeping Russian Tortoises on and off since at last 2010 and steadily for almost 3 years now. In all of that time, I have never, and I do mean never, seen any of my Russian Tortoises drink. I do not leave a water bowl or dish in the enclosure with them because of the defecation factor and me maybe not being there to change the water immediately; so, I put them in a large tub of shallow water at least three times a week, sometimes up to 5 times a week. I have observed them carefully while in the water. They soak, they defecate, they urinate but they simply do not drink. That includes at least 6 Russians that I have kept (maybe 7), including the 3 I have currently. My other current tortoises are a mated pair of Hermann's, a baby Hermann's and a Redfoot adult - all drink readily. I also have had a several other Hermann's and a few other Redfoots and all drank on a regular basis.

I am guessing that the Russians get enough water from what they eat. but am wondering if them not drinking is normal. They are apparently healthy, eat well, have good weight, etc.. Has anyone else noticed this lack of drinking relative their Russian Tortoises?

Thanks,
GB