Each bowl should be big enough for your largest crab to climb in to. If smaller crabs within the cage might have a challenge getting in and out of the water dishes, a small natural sea sponge
can be placed into each dish to act as a safety bridge to prevent drowning.
Hermit crabs use the water to drink, bathe and replenish their shell water (extra water they carry within the back of their shell). By providing both fresh and salt water you are letting the crab decide for themselves what they need.
Use bottled or de-chlorinated tap water for their Fresh water supply. Chlorine found in tap water is harmful to hermit crabs. In order to make tap water safe, de-chlorination drops can be used to remove Chlorine. Using bottled or distilled water is probably easier and cheaper than adding de-chlorination drops.
Use distilled water mixed with aquarium salt such as Oceanic Salt
to make salt water. Do not use table salt
, it contains iodine which can be harmful to crabs.
For crab owners that have well water, I still recommend using distilled water. Some wells use a salt softening system or have higher levels of minerals. When mixed with the additional minerals in aquarium salt an unknown and possibly unsafe level of salt and minerals could result. By using distilled water you are begining with water that you know has nothing additional in it.