Learn Spanish (Latin America): Hay que mantener los cuartos limpios.

Hay que is used to talk about rules or things that generally need to be done, without saying exactly who has to do them. It translates to 'one has to' or 'it is necessary to.' If you want to say a specific person has to do something, you use a form of tener que, like tengo que (I have to).

Why is the verb mantener not conjugated?

The phrase hay que must always be followed directly by an infinitive (an unconjugated verb ending in -ar, -er, or -ir). That is why we use mantener (to keep) right after it.

Why is the adjective limpios at the end of the sentence instead of before cuartos?

In this sentence, limpios describes the state the rooms must be kept in. It works just like the English translation: we say 'keep the rooms clean', not 'keep the clean rooms.'

Why does limpios have an 's' at the end?

In Spanish, adjectives must match the noun they describe in both gender and number. Because it is describing los cuartos (which is masculine and plural), the adjective limpio changes to limpios.