Term for a word without a singular

A word like "water" can’t be introduced by an indefinite article unless one adds a qualifying word (a water droplet). Grass is like this (a blade of grass, not "a grass" with grass being a noun). The use of the definite article seems to presume talking about a group or a pluralized, collective idea (implying the introduction of a preposition "of" after a ‘none some all’ qualifier – all OF the water, which means that ultimately, one is speaking about the plural grouping of that which can’t be spoken of in the singular).

Is there a term for a word that can’t be spoken of in the indefinite singular?