The missing "a" in one example

Question

Please explain why the example "Nos han dado de beber porque ..." is not written as

"Nos han dado de berber a nosotros porque estábamos exhaustos...".

In other words, why is the "a" missing in that particular example?

Gracias,

Pati Ecuamigo

Silvia Píriz · Accepted Answer

Hola Pati E.
Thank you for your question.
In this example, the indirect object is already expressed by the pronoun nos in Nos han dado de beber..., so there is no need to repeat it with a nosotros.
The sentence:
Nos han dado de beber porque estábamos exhaustos.
is completely natural and means "They gave us something to drink because we were exhausted".
You can also say:
Nos han dado de beber a nosotros porque estábamos exhaustos.
but adding a nosotros is optional and is generally only used for emphasis, contrast or clarification (for example, if you want to distinguish us from someone else).
So the a is not actually missing, rather, the indirect object is already expressed by nos, making a nosotros unnecessary in this context.
Un saludo
Silvia