Indefinite Article With Uncountable Noun
Uncountable nouns are nouns which are difficult or impossible to count. Uncountable nouns include untouchable things (information, air), things like liquids (milk, wine), and things which are too large or numerous to count (equipment, sand, wood). Because these things can’t be counted, singular articles like a or an should not be used to modify them. Uncountable nouns can be modified by words like some. Alternately, the uncountable noun can be changed to a countable noun.
Please give me a water.
Water is an uncountable noun, and should not be used with the indefinite article, a.
Please give me some water.
Please give me a bottle of water.
Please give me an ice.
Please give me an ice cube.
Please give me some ice.
N.B. Depending on the context, some nouns can be countable or uncountable (e.g. hair, noise, time)
We need a light in this room.
We need some light in this room.