I've been doing a lot of research on plant nutrition lately, and have learned that we have all been right AND wrong about both urea and foliar feeding - which I always regarded as a waste of time.
According to my reading (Marschner - Mineral Nutrition in Higher Plants), more-polarized species - nitrate and ammonium ions being relatively highly so - are mostly blocked from entering leaves, but are preferentially absorbed by the roots. Less-polar species like urea however, can be absorbed directly through the leaves, but are mostly blocked from root absorption, hence the need for it to be decomposed first. You will find that fertilizer products intended to "green up" a crop, usually have urea in them for rapid leaf uptake, and WOW! do they work fast.
Unfortunately, many epiphytes, and especially orchids, in an effort to reduce potential water loss through the leaves have developed physiologies - including thick coatings - that reduce the transfer of much of anything through the leaves. Not eliminating it, but reducing it to a fract of that seen in terrestrial plants.
The pure water formula is 12.5% nitrate, 0.7% ammonium. The "Well Water" formula is 13.6% nitrate, 5.7% ammonium