Does the "Electric Fresh & Clear Drinking Fountain for Cats for Dogs" have to be constantly switched on?

We've just bought an electric Fresh & Clear drinking drinking fountain for our cat. Does it have to be permanently switched on 24/7 for it have any benefit or just for long enough for the water to filter through once? Also, should it be switched on whenever the cat's drinking from it? I know that with... show more We've just bought an electric Fresh & Clear drinking drinking fountain for our cat. Does it have to be permanently switched on 24/7 for it have any benefit or just for long enough for the water to filter through once? Also, should it be switched on whenever the cat's drinking from it? I know that with water filter jugs used for human consumption, once the water's filtered, that's it - job done.
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