"Uisge" is just a different way of spelling "whiskey"; and it just means water. That must get confusing sometimes if you do just want a drink of water in a Gaelic speaking community...

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Hard water is water with various stuff like sodium and magnesium dissolved in it. Furs up the domestic plumbing, but on the whole it's good for the plumbing in the body, because you need that stuff, and it tastes better. Remove the chemicals and it's called soft, and its better for washing and worse for drinking.

People often have water softening devices in their domestic plumbing systems, to save money on washing and plumbers. Then they have to pay for the water they drink in a bottle. You pays your money and you takes your choice.

Whether the water in your area is hard or soft will depend on where it's come from, and how it's been treated, either by the water company, or in your own system.