Although they may not prefer it, both of the speices of land hermit crabs discussed on this site MUST be bathed in freshwater by their owners on a weekly basis, but not more. In the wild, rain and accidental falls into puddles are--although inconvenient--critical to a crab's well-being. A bath not only inspires them to wash themselves, but it replenishes their shell water, cleans the gills, loosens sand or food debris lodged between the exoskeleton joints, and removes any waste products that may be stuck inside the shell.

To bathe your crabs, use a non-metallic container. (Metal containers cause metal ions to leach into the water which can damage a crab's gills.)

Gently but quickly submerge the hermit crab in the water. Dunk the crab 3 times, with each dunk lasting 2 to 5 seconds.

DO NOT LEAVE A CRAB UNATTENDED WHILE SUBMERGED IN WATER. Hermit crab gills are NOT like fish gills. Extended submergion can cause brain damage or death.

Do not bathe your crab more often than as recommended above, since doing so would deplete the exoskeleton of its protective coating and soften it.

To rinse the inside of the shell, submerge it into the water with the opening facing up, keeping the majority of the crab out of the water. Then dump the water from the shell and allow the crab to air dry.

Some recommend the use of Stress Coat, an aloe vera and water dechlorinizer liquid that helps aquarium fish repair damaged scales. When mixed into the bath water, a hermit crab's exoskeleton will benefit. Use 1 to 3 drops per gallon of water. Never create a solution more than 24 hours before the bath, since aloe vera decomposes quickly and bacteria can form. Do not put Stress Coat into your crab's water dish, as it should not be consumed any more than the tiny bit your crab might sample while in the bath.

Allow your crab to air dry while walking on a clean towel before returning her to the tank. You may notice that your crab will rub her legs together to keep herself clean.
Peanut carefully holds onto my thumb as she is about to get her shell dunked in a solution of dechlorinated freshwater with a drop of Stress Coat.