Canned water is drinking water, including spring water, artesian spring water, purified water, carbonated water and mineral water, packaged in beverage cans made of aluminium or tin-plated steel. … Some companies have launched water in cans, offering a more environmentally sustainable alternative to plastic bottles.

Why doesn't water come in a can?

Because cans for liquid beverages are originally designed to keep the gasses inside. Water doesnt generate that much gas that it needed to be put into a can to hold the pressure, so if you dont need to put it in a can, why would you?

Why don't they sell water in aluminum cans?

Primarily cost is the reason. Cans are much more expensive than plastic bottles. Water, lacking any carbonation, doesn’t exert any significant pressure on the container so you can use VERY thin plastic to hold it.