Depends on what machine we are talking about
Enough water us when the washer can move water through the laundry sufficently enough.
When the washer has no aid in water movement besides the drum, you need enough for all the laundry being pulled through it.
Without scooping vanes, a recirc or slanted drum vanes which move laundry ccloser to the drum more towards either the front or the back and thus allow laundry from the core to move to the outside, water levels need to be high.
If there are scooping vanes, more water is "filtered" through the entire load thus reducing the needed waterlevel.
With a recirc, water levels drop again.
With lower water levels, detergent concentration rises thus reducing cycle time and necesarry mechanical action.
TLDR there is no one needed water level. Move water through laundry as much as possible.
How dosen't matter.
Who ever used a high capacity HE machine and filled it to the brim can testiment that: A (well designed and programmed) recirculation spray allows for faster, better cleaning and far far supirior rinsinging.
For hospitals there are sanatisation requirements. They aren't even concerned of cleanlines in terms of stain remival, but pure bacteria reduction.
The manufacturer tjen designs specific requirements and cycles for its machines to match needed standards, depending on how the machine is designed.
In hotels actually its the other way around, kind of. There is not set standard, thus, machine manufacturer and hotel usually play together to reach the desired level of results while minimizing usage.
For example, the manufacturer knows that its machine only needs 1.5gal per pound of flat bedding of a certain kind for the mainwash (numbers being just random). Thus, they programn to run a Hot Normal cycle with a certain load detection and reaction pattern.
If the hotel however knows for example its bedding needs a certain amount more water, but as they do not use starch, they need less water in the final rinse, the service tech who installs the new machine can tweak the cycles to correspond with that need.
If it turns out the new machine still needs different parameters (for example one rinse less entirely), the owner/supervisor is usually tought by a service tech how to change such parameters in case of linen or detergent change ir simmilar.
For householduse, you have to estimate an everage customer and its usage pattern and the design one or a few cycle that match those use cases plus as many more ascpossible. That design then is fixed, for at least one, but often even more itterations of the same machine.
You can't teach a costumer to reprogramn their machine due to liabiloty issues, and people don't have the will to pay for a service tech to come and reprogramn their cycles (if that even is posdible) and pay 159 bucks or such for that.
Thus often, washer controls are designed as read only due to cost reasons.
Itterations only happen with new machines.
However, hers in Germany at least, its common to find reprogrammable PCBs. Should there be major issues or minor fixes, the manufacturer pushes a new software for an appliance every few months or years.
If there is a service call then, while the technician writes his bill, his PC is just hooked up to the machine and installs the reworked software.
But even then, most customers don't even kniw that is possible or don't pay extra just for that service and thus it often only happens as a side-service during major other works.