Indoor and tabletop fountains became enormously popular several years ago. The appeal is easy to see - the sound of water gently falling into water is soothing to the nerves, and a fountain adds freshness and humidity to stale, over-conditioned indoor air. Soon tabletop fountains were everywhere.
The latest innovation to the standard water-recirculating fountain is the addition of a mister, or fog-maker; this will cause a mist to form on the surface of the pool of water that looks and acts like low-lying fog. Some misting fountains include underwater lights that change color, to give the mist an ethereal glow.
The fog-making unit in a misting fountain is quite small and simple, and is the same device that makes mist in ionic air purifiers. It uses no chemicals like dry ice; instead, it makes ultrasonic vibrations in the water itself. This changes the surface tension of the water - the force that allows tiny bugs or leaves to rest on top of the water rather than sinking; the lower surface tension causes some water droplets at the surface to escape into the air. So the mist you see is nothing but water, like natural fog or morning mist.
You can purchase fountains that come equipped with misters, or add a mister to your existing fountain. Because the ultrasonic vibrations produce negative ions, a misting fountain will purify area in its vicinity in the same way that an ionic air purifier does, so they're perfect accessories if you have allergies or asthma. Since there's nothing in the fountain or the mist but water, you needn't worry if your pets are fascinated by the mist, as most cats will be. I have even used a mist-maker in our indoor fishpond. The fish seem to enjoy it and will congregate around the unit, and hide under the cover of the mist.
You will have to be careful where you place your fountain, however. The mist is water, after all, and condenses. You may find that tendrils of mist may creep out over the rim of your fountain's bowl, so don't place a misting fountain on a treasured antique table without protecting the surface first. This should be done in any event, since all fountains occasionally splash to some degree.
Follow the directions for care of your misting fountain; it needs occasional cleaning to work properly. Then enjoy the gentle splashing of water as you watch the mist curl and twist over the surface of your tiny pond.