Classic frying is not recommended as fats change their properties. Heated oil may have detrimental effects on health as heating produces harmful products of lipid peroxidation, which are believed to be responsible in the pathogenesis of many diseases like cardiovascular disease and cancer.
Therefore the oils, if any, should be consumed cold-pressed and you can very satisfactorily fry on water.
Once you have mastered water-frying onions and other vegetables, it suddenly turns out to be pretty easy. Like in any other activity, here as well, practice makes perfect. Vegetables can be caramelized using water instead of oil. But it is true that using water is a bit more time-consuming.
Put about half a deciliter of water and vegetables into a pan. Use medium to strong heat. When water evaporates and vegetables start to brown lightly and caramelize, add a little more water. Keep stirring the vegetables all the time. Repeat the procedure a couple of times until the vegetables are completely caramelized. A piece of cake, isn't it?