Throughout the Land of Fate there's a custom that if a host gives salt to a guest, they commit to not harming each other for three days. After three days after the latest shared meal, the bond is over.

This goes for all Enlightened Beings, regardless of what side they are on in any local wars. Pirates and tyrants alike follow this rule.

There are stories of a burglar breaking in to a home, accidentally tasting some salt, and then leaving without taking anything.

And, it's often accepted to extend to any food or water, coffee, bread etc.

For more information, see pages 17-18 in 2e Arabian Adventures.

All Enlightened Beings (which includes you guys) are well aware of this tradition.

In game terms, for the purposes of this campaign, there's no supernatural "forcefield" or mind control that makes your character follow this tradition. But there is a supernatural consequence for breaking it. (Permanent -2 on all rolls, throws and checks, and a negative or at best indifferent reaction from all strangers.) Remove Curse spells work fine to remove this curse.

This supernatural aspect applies to salt specifically. But your upbringing and custom have taught you that it applies to all food, drink and water.