Breakdown of Yo sirvo la ensalada mientras tú hierves el agua en la olla.
yo
I
tú
you (informal singular)
en
in / on / at
el agua
water
Questions & Answers about Yo sirvo la ensalada mientras tú hierves el agua en la olla.
Why is it el agua if agua is a feminine word?
Even though agua is feminine, it starts with a stressed 'a' sound. To avoid the awkward sound of saying la agua, Spanish uses el in the singular. If it were plural, it would use the feminine article: las aguas. Any adjectives attached to it also stay feminine, like el agua fría.
Why do both verbs in this sentence have spelling changes in the stem (sirvo and hierves)?
Could we use the subjunctive after mientras here?
Not in this specific case. When mientras means 'while' and describes two concrete actions happening at the same time in the present, you use the indicative mood (like hierves). You only use the subjunctive after mientras when it points to an unknown future condition, meaning 'as long as'.
Why are the subject pronouns yo and tú included here when Spanish normally drops them?