Still water is water that doesn’t have any fizz to it.
It may be tap water, may be bottled water, it may be spring and / or mineral water.
The opposite category is sparkling aka carbonated water.
Still water in bottles has been increasing in popularity over sparkling water. It’s seen as a healthier alternative to soft drinks, and as more efficacious when you’re thirsty than sparkling water.
In some areas, such as Italy, there’s a growing tendency to use bottled, still water in cooking.
Some still waters are marketed with vague health benefits (such as being free from unhealthful attributes); others are marketed as out and out mineral waters with positive health benefits.
Some makers try to extend their product lines by flavouring it — putting it in the soft drink range — or by fortifying it with things such as calcium.
93% of the water drunk in America (as of 2005) is still water.