Lavar or Lavarnos

[Rusty]

When the action reflects back to the subject, the reflexive pronoun is necessary.

Tenemos que lavarnos las manos. = We have to wash our hands.

Even though the definite article 'las' appears here, it is understood to be the same person as the subject. Here, 'las' must be translated as the possessive adjective 'our', since the subject is 'we'.

Tengo que lavarme las manos. = I have to wash my hands.
Tienes que lavarte las manos. = You need to wash your hands.
Él tiene que lavarse las manos. = He needs to wash his hands.


If the person who needs their hands washed is NOT the subject, we don't use the reflexive form of the verb.

Tenemos que lavar las manos de él. = We have to wash his hands.
Tenemos que lavar las manos de Miguel. = We have to wash Miguel's hands.
(We may refer to anyone other than ourselves this way, by name or by using a pronoun that identifies that person to those involved in the conversation. We can also choose to use an appropriate-to-person possessive adjective.)

Tengo que lavar tus manos. = I have to wash your hands.
Tengo que lavar sus manos. = I have to wash his hands.