I am a Spanish tutor in Phoenix, Arizona, and my students always ask me: is it el agua or la agua? El arma o la arma? …. Is agua a feminine or masculine word? The answer is simple.
The masculine singular article el is used before nouns beginning with a stressed a for reasons of sonority. Feminine nouns such as agua, álgebra, águila, are preceded by the masculine el instead of the feminine la in order to avoid the awkward sound of la … a. For the plurals of these feminine nouns, however, the feminine plural form las is used. Nouns that begin with a silent followed by a stressed a follow the same pattern.
Here are more examples:
Stressed a
Singular Plural Singular Plural
el área las áreas la albóndiga las albóndigas
el alma las almas la arteria
el hacha las hachas la hamaca las hamacas
el águila las águilas la almohada las almohadas
REMEMBER: The noun ending is not the most reliable indicator of noun gender. The article that precedes the noun always indicates the noun gender except in the case of nouns beginning with a stressed a or ha.
Also remember in Spanish, all adjectives must agree in number and gender with the nouns they modify. Study the following examples:
el agua fría, las aguas frías
el alma pura, las almas puras
el hacha afilada, las hachas afiladas
el águila robusta, las águilas robustas
As far as the indefinite article, the use of “una” is not considered an error. However, the use of apocopated forms “un” is preferred when they precede the noun. If there is another element between the indefinite article and the noun, the complete feminine form is used again. So, one would say “un agua fresca” pero “una fresca agua”.