We learn that it is forbidden to walk a distance of four amohs without washing the hands except in cases of extreme necessity. However, the Metsudah Kitzur Shulchan Aruch in a footnote states that "Within the house you may walk even more than four amohs to get water for washing." What could be the source for this exception? It is not given in the Kitzur.

The Shlah Hakadosh writes that one shouldn’t walk more than four Amot without Netilah. The Mishna Brurah (1, 2) brings an opinion (Shevut Yaakov) that the whole house is like four Amot for that matter however better not to rely on that opinion unless necessary.