All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
In principle, the maid has no right to use the working hours upon which the contract of hiring is concluded with her (i.e. from 9 am to 5 pm) for her own purposes or to use the water in the house where she works without the permission of its owner. However, we think that this matter should not cause a dispute between you and your husband. If there is any harm that may be resulted from the maid washing her clothes in your home, then you should let your husband know about it, as this is a means of convincing him and getting his consent. Nonetheless, if there is no harm from this, then it is not among the good morals to prevent her from washing her clothes in your house.
Furthermore, if your husband is the owner of the house and he pays the water bill, then you have no right to prevent the maid from washing her clothes if he allows her to do so.
For more benefit, please refer to Fataawa 83374 and 92230.
Allaah Knows best.