After thinking about it I'm starting to think those frogs in Zora's domain are to blame for the addictive and drug-like properties of the water (Although the concentrated Zora Butt blend might still be a reason it has a unique... taste).
Certain frogs and toads in reality excrete liquid from their pores that if injested can cause hallucinations (This is why it was a common practice for ancient peoples to lick frogs and toads... of course the danger is that it's a toad or frog that excrets poison, so I wouldn't suggest licking a toad or frog to get high, you might die instead). The King Zora suggested that he was providing the lakeside labrotory scientist with frogs, sure their eyes are used for eyedrops but I'm pretty sure there was a purpose for the rest of the frogs. Probably what happened was the lakeside scientist began stocking up on product. When Zora's domain froze over he began selling the frog juice to be injected into the cows at Lon Lon ranch by Ingo, whom Ganondorf put in charge of the ranch (All three were in on the drug ring, they all probably have addictions to the “product” also. I think the lakeside scientist probably injects it straight up like Herion).
This would explain why the Hylians easily transitioned from Zora Water to Lon Lon Milk, it induces the same “high” and fufills their addiction because it actually contains the same substance they became dependant on.