Should all valves subject to vacuum conditions have water seals (or metal bellow seal) as an option?
Generally no. But you have to specify with details to get a proper answer: exact vacuum (figures), application, industry type, valve type, valve size, other requirements, and eventually local regulations.
Most important is that the valve selected is constructed and tested for ALL conditions that you have: both vacuum, overpressure, tightness (under given conditions), and have references to prove trouble free operation over time.
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