Mineral water is water containing minerals or other dissolved substances that alter its taste or give it therapeutic value, generally obtained from a naturally occurring mineral spring or source. Dissolved substances in the water may include various salts and sulfur compounds. Mineral water can be sparkling (with effervescence), or still (without effervescence).

Traditionally, mineral waters were used or consumed at their source, often referred to as "taking the waters" or "taking the cure," at sites such as spas, baths or wells. The term spa was used for a place where the water was consumed and bathed in; bath where the water was used primarily for bathing, therapeutics, or recreation; and well where the water was to be consumed. Active tourist centres have grown up around many mineral water sites since ancient times, such as Vichy (France), Jermuk (Armenia), Yessentuki (Russia), Spa (Belgium), and Bath (England). Tourist development resulted in spa towns and hydropathic hotels (often shortened to "hydros").

In modern times, it is far more common for mineral waters to be bottled at source for distributed consumption. Travelling to the mineral water site for direct access to the water is now uncommon, and in many cases not possible (because of exclusive commercial ownership rights). There are more than 3,000 brands of mineral water commercially available worldwide.

The more minerals in drinking water, the harder it is said to be; water with few minerals is described as being soft.

The U.S. FDA classifies mineral water as water containing at least 250 parts per million total dissolved solids (TDS), originating from a geologically and physically protected underground water source. No minerals may be added to this water.

However, in many places, the term "mineral water" is colloquially used to mean any bottled carbonated water or soda water, as opposed to tap water.