Distilled water is excellent also. In the Jewelry Industry, manufacturers of the best ultrasonics recommend it. Tap water for the most part is chlorinated. Set out for 24 hours the chlorine evaporates out, then boil if you want to. Chlorine will weaken even karat gold alloys with prolonged and repeated contact/use (we are talking prolooooooooooooooooonged here). Cleaners/solvents containing ammonia will also affect or haze the finish on aluminum alloy parts. The work, for the most part, is done by the machine, not the additive to the water. A few drops or a small squirt (depending on machine size) is plenty to break down grease etc., the machine does the rest. I use DAWN or a non ammonia Jewelry concentrate. I'm sure there are others. Distilled water is also the best for your steam iron, clothes steamer or Submarine as it does not tend to corrode/clog inner parts.
Also, the solution does not need to be changed for each use. Just change it when it gets really dirty or sludge accumulates at the bottom of the tank.
And, suspend parts or raise them slightly from the metal tank bottom. Metal to metal vibration in the tank will create abrasion marks on items. Stiff, plastic coated wire bent to shape works well. An "S" shaped hook or long hanger across the tank.
Finally, if you are seriously considering the purchase of one: $25-$50 (your wife's jewelry and the occasional bike part), $50-$100 (a little more serious), $100-$200 (getting to the his and sometimes hers), $200-up (get one with a heater and maybe a drain plug). I've used all the categories. You get what you pay for. Think about your current and future needs.
Occasional hobby/short use may not require all of this.
Jay "20+ years of listening to and using one at work almost daily" Dubiel Halifax, VA USA