Interesting, I don't think it does here other than extreme minority of cases - because it's just not standard plumbing. You typically have a washing machine & dishwasher hookup & waste under the sink; it's pretty standardised and it's on cold.

> As an example Frigidaire, GE, KitchenAid, Whirlpool will only work with hot water

Yeah, afaik without actually looking into it, of those only Whirlpool is distributed here (KitchenAid stuff yes for sure, but not I think dishwashers) and as above I'm pretty sure they must be different models, just like LH/RH driver cars.

Of course you can import whatever you want, but then you should probably expect to deal with some such plumbing (and potentially electrical, at very least changing the plug) oddities.

How do you handle softened water in the UK?

In the US, it's common to have a water softener on the hot water line, intended to soften the inputs for appliances and showers. The cold water line is not softened, to avoid drinking sodium-laced water.

I wouldn't like to estimate an installation percentage, but it's probably not quite 'standard' to have at all. In the systems I've known, I believe it's been on the cold-water line pre-boiler; in the scullery with the sink there pre-softener so you get one (cold) tap without.

I don't claim authority on the matter though.