Why Do I say ´el alma´ if ´alma´ is a feminine word??

Grammar Genius,

Why do some words like ´agua´ and ´alma´ become masculine in their singular form? How do I know which words follow this rule?

Many times, there is doubt over whether to say 'esta aula' or 'este aula'; 'este agua' or 'esta agua'. The rule is the following: only the articles el, un and the indefinites algún and ningún proceed in masculine form feminine nouns that begin with the accented a (ha).

The rest of the determinants (and adjectives) following their normal feminine form. For example:

El alma (agua, hacha, asa, aula…)
Un alma (agua, hacha, asa, aual…)
Algún alma (agua, hacha, asa, aula…)
Ningún alma (agua, hacha, asa, aula…)

Also:

Esta alma (agua, hacha, asa, aula…)
Esa alma (agua, hacha, asa, aula…)
Aquella alma (agua, hacha, asa, aula…)
Toda alma (agua, hacha, asa, aula…)
Poca hambre
Mucha hambre
Primera aula
Tercera aula

The following are INCORRECT:

La alma (agua, hacha, asa, aula…)
Una alma (agua, hacha, asa, aula…)
Alguna alma (agua, hacha, asa, aula…)
Ninguna alma (agua, hacha, asa, aula…)

Keep in mind the following observations:

The rule is not valid for adjectives that begin with the sound a (ha):

La áspera corteza (and not el áspera corteza).
La agria naranja (and not el agria naranja)

In their plural form, their normal form is used:

Las almas
Unas almas
Algunas almas

If between the article and the noun another word is inserted, the normal feminine form of the article should be written:

La cristalina agua (not el agua cristalina)
La auténtica hambre (but not el hambre auténtica)

An excpetion to the rule:

La hache (but not el hache)

Words that begin with the a sound but are not accented do not follow the rule:

The following are incorrect: el Alhambra (correct: la alhambra), el harina (correct: la harina), or el acné (correct: la acné)