Why Soak? by Darrell Senneke
I ask this because there is more involved here than just drinking. And yes, I do soak all my torts even those with access to water. I soak my adult tortoises about once a week. The babies are religiously soaked daily. Please note all this is again in "indoor" accommodations. Outside they can set up their micro climate so such frequent soaks are not as necessary.
The following explanation of why I think that babies must be soaked.
A quick physics lesson: We all know that tortoises (box turtles too!) set up micro climates for themselves where the humidity is higher than the ambient. If you doubt this, just compare the relative humidity in a "resting form, pad or scrape" to the general humidity in the open. These animals have evolved to be in tune with a specific environment which consists of utilizing these "pads". A large tortoise because of his volume to surface ratio has more resistance to lack of humidity than hatchlings.
For example - let us assume for the ease of calculation
that a tortoise is shaped like a cube. A 1-inch hatchling
would have a volume of 1 cubic inch but would have a surface area of
6 square inches giving a volume-to-surface ratio of 1/6 or
0.1666. A 4-inch tortoise would have a volume of 64 cubic inches
but a surface area of 96 square inches for a ratio of 64/96 or 0.666
a difference of 4 times as much volume to surface. To take
it to extremes a 12-inch tortoise would have a volume of 1728 and
a surface area of 864 for 1728/864 or a factor of 2.0. Looking at it this
way it is easy to see how a hatchling becomes dehydrated much much easier
than an adult simply because his surface area is so high compared to his
volume, or reserves. It is also easy to see how adults generally
are more tolerant than hatchlings of conditions that are not "tuned" for
them. I do realize that tortoises are not cubes but the same results
will be manifest if one does a water displacement of them to measure
volume and carefully measures surface area as best they can.