Here in the Twin Cities metro area it's standard procedure to run a separate water line for un-softened cold water to the kitchen. I don't like it, and I think this trend ought to change.
When I used to live in Minneapolis, this was a non-issue. Minneapolis has great water, and there is no need for a water softener at all. When I moved to Maple Grove, living without a water softener simply wasn't an option. The water up here is very hard and will leave deposits over everything and gunk up the faucets very quickly. A working water softener is important.
Much to my annoyance, the cold water to my kitchen wasn't softened when I moved in. Visit just about any home built in the Twin Cities over the last thirty years, and about 80% of any other homes that have water softeners, and you'll find the same to be true. The cold water line to the kitchen bypasses the water softener on purpose. Plumbers actually go out of their way to do this.
I've had plumbers outside of the metro area tell me that this is no longer being done, but this is almost all that I ever see on new construction homes here in the Twin Cities. This is still standard practice.
Why the cold hard water to the kitchen
I've asked a lot of plumbers about this, and they've all given me the same answer; it's an option. Some people like the option of having hard water available, both for consumption and for watering plants. I guess you're not supposed to water your plants with soft water.
As for consumption, the idea is that we already get too much sodium in our diet, and we shouldn't be getting even more from our water.
How much sodium is added to softened water? According to Pure Water Products, LLC, the amount of sodium added by a water softener depends on how hard the water was to start with. Here in Maple Grove, the water hardness ranges from 22 grains per gallon (gpg) to 25 gpg. To make it really simple, they say to multiply the grains of hardness by 1.89, and you have the total mg of sodium that is added to water through the softening process in one 8 oz glass of water. In other words, an 8 oz glass of softened Maple Grove water would have 25 x 1.89 mg of sodium, or about 50 mg.
To put that into perspective, a single slice of Brownberry® whole grain Outnut bread contains 150 mg of sodium. It's not nothing, and if you drink 50 glasses of water a day (or whatever number the experts are recommending these days), that can add up to a lot of sodium. Maybe.