Audiodesk pro with only water

Ultrasonic cleaning machines definitely will work with just plain water. A lot of what cleaning solutions do is keep the crud cleaned off in solution so it doesn't just stick back on the record and will rinse off easier. A rinse with a little extra water or a wipe would do about as well. The cleaning solution also helps with some things that don't dissolve so well in pure water. But a little extra time in the machine will take care of that as well. So its not as efficient but yeah you will be fine with just distilled water.

Distilled water alone is not enough! You need to add a surfacant to release the H2O's inherent surface tension! A small amount of a glass cleaner (Windex) will do just as well as any premium record cleaning fluid. That's what I use - with sparkling clean results (after a final rinse with plain distilled water).

The primary cleaning mechanism for the Audio Desk is its four brushes; ultrasonic action helps but is secondary. 

Use with distilled water alone likely gets a record cleaner than it was but not as clean as use with the ADS surfactant.

If your unit is still under warranty, anything other than the ADS fluid will void the warranty.  If the warranty has value to you, just use distilled water.

If it is out of warranty you can try two drops of dish detergent (eg, Dawn) along with 1/4 teaspoon of a rinse agent such as Ilfotol.  If you do that I would not let the ADS dry the record because it will dry with detergent water (soluble particles) on it.  Drain the tank and refill with distilled water only, then run a full cycle.  You could clean say 5 records with detergent water, all without drying - put them on a dish rack - then fill the tank with distilled water only and run each through a cycle with drying.  Distilled water is cheap.

The ADS is designed for use with the ADS surfactant.  People do what they choose, though optimal cleaning comes from using the machine as designed.