In some places my hands still feel soapy after rinsing for a full minute — what is different about the water?

You have moved from hard water to soft water, and the surprise is that soft water is the one behaving correctly.

Hard water contains dissolved calcium and magnesium. Those react with soap to form an insoluble scum — the grey ring in a bathtub, the film on a shower screen. That reaction consumes soap, which is why hard-water areas need more of it to lather, and it also strips the remaining soap off your skin quickly, which is what you have learned to interpret as "rinsed".

Soft water has almost none of those minerals, so nothing destroys the soap. It stays dissolved, keeps working, and continues to make your skin slippery until it is physically washed away by volume.

So the slippery feeling is not leftover soap sitting on you so much as soap doing its job in the absence of anything to stop it. People moving in the other direction, from soft to hard, complain that soap will not lather and their skin feels tight and squeaky — the same difference read from the other end.

For the practical half, two things genuinely work and one does not.

Works: use less soap. Much less than you are used to. In soft water a bar lathers with a fraction of what a hard-water area needs, and most of the slipperiness is simply excess. Halving the amount usually solves it outright.

Works: finish with something slightly acidic. A rinse with very dilute vinegar or a squeeze of lemon neutralises the residue immediately. Overkill for hand washing but genuinely useful for hair, which is where soft water surprises people most.

Does not work: rinsing for longer. You have already discovered this. Past a few seconds the extra water is not achieving anything, because the problem is quantity of soap, not duration of rinse.

Since you travel: the other thing to be ready for is the reverse trip.

Moving from a soft-water region to a hard-water one, expect your usual amount of shampoo to produce almost no foam, your skin to feel dry, and a kettle that furs up in a fortnight. People often blame the accommodation's plumbing when it is simply the local geology.

Rough rule: limestone and chalk country gives hard water, granite and upland country gives soft. Ireland and Scotland's west, much of Scandinavia and the Pacific Northwest are soft. Southern England and much of the American Midwest are hard. It is one of the few things about a destination that reliably changes your bathroom routine and never appears in a guidebook.

One more that is worth saying because it sounds like a workaround and is actually the fix: a syndet or liquid cleanser rather than a true soap bar behaves the same in both water types.

Traditional soap is the thing that reacts with hardness minerals. Detergent-based cleansers do not, so they lather consistently, rinse consistently and leave no scum anywhere. If you move between water types often, that single swap removes the whole problem in both directions.