The relevance of beer with regard to water conservation and safe consumption is _not_ because the alcohol sterilizes the fluid. It's because successfully brewed and unfiltered beer forms a relatively stable ecosystem of unproblematic yeasts and lactic acid bacteria which prevent other unsafe micro organisms to take over and multiply. The hop is actually contributing to chemical conservation, though.
Alpha-Amylase conversion is optimal (for beer production) at about 140 F/60 C. Second and third extractions occur at about 155 and 175 F, respectively, well below the boiling point.
More importantly, the first extraction only marginally reaches pasteurization temperatures (using low-temp long time parameters), so the majority of liquid in beer inhibits, but does not completely kill, pathogens.
If we're talking about medieval beer production, it certainly started with boiling the water.
In absence of temperature measurement, they would time how long the water had been off the boil before it would be used.
They also commonly believed that the boil was integral to the carbonation in the final product. That the amount of time spent boiling the water correlated to more bubbles in the beer, and would often do things like boil the water until it was half gone.
Hops came into use relatively recently, I think? Not yet popular in Britain by the 1500s, anyway. Though used in Holland by that point, and possibly the predecessor (a mixture of herbs called gruit) was antibacterial anyway.
I'm not clear what you mean by "contributing to chemical conservation". They don't conserve anything, really.
Hops are antibiotic and antifungal in nature. That, combined with their mild flavor (compared to things like wormwood), is why they are synonymous with beer production today.
