They do not list charges or uses per day. Only that the first Elemental has to die (or be dispelled or dismissed) before a new one can be summoned. The summoning only requires one round so you could essentially keep summoning huge Elementals and send them to attack a small fort or town one by one until they crush it and all defenders. With enough mobility and sneakiness you could destroy a string of targets every day.
I mean items like Bowl of Commanding Water Elementals, Brazier of Commanding Fire Elementals, Censer of Controlling Air Elementals, Stone of Controlling Earth Elementals.
Here's a link to all:
http://www.d20srd.org/srd/magicItems/wondrousItems.htm#bowlofCommandingWaterElementals
PS: Do the Elementals summoned have a duration? It says:
A new elemental requires the bowl to be filled with new water, which cannot happen until after the first elemental disappears (is dispelled, dismissed, or slain).
Doesn't mention duration ending, or expires.
Best Answer
Yes, they work an infinite number of times, and yes they have a limited duration, as well as limitations on targeting and range, rules for dispelling, and so on. These are all covered by the statement that “in all ways the bowl functions as the summon monster VI [or VII if salt is used] spell,” excepting, of course, the specific limitations of the item (i.e. only one at a time, only elementals of that size, number, and element). The entire point of that statement is to avoid having to rewrite all the rules of the spell here in the item; they still apply.
For what it’s worth, for the price, that’s a really weak effect. 100,000 gp should be able to do more than maybe wear down a small fort.
As a comparison, summon monster VII as an at-will, command-word item costs 182,000 gp, and thus for less than twice the price, you could get thirteen times the effect (creating one huge elemental per round, each lasting thirteen rounds because of the caster level of the item).
But that still wouldn’t be very effective; at the levels where you can afford these items, huge elementals just aren’t that impressive.