Agua (water)
Agua (water) ends with an "a". Why is it el agua and not la agua?
3 Answers
When singular most words that start with the letter "a" use the masculine article "el" even though the word is actually feminine.
The reasoning is this: La agua, when you say it out loud, would sound like "lagua."
So, to differentiate the word and the article attached to the word we say "el agua."
However, when plural, if you were to say "the waters" it would be "las aguas." because the "s" in "las" will not cause a funny mixing of the words that la and agua do.
See previous answers to this question if you are still confused.
If you search the forum for "agua" you will get pretty much nothing else but answer threads on exactly your question.
Link didn't work, sorry.