There are two aspects to niddah: issur (forbidden physical contact) and tumah (ritual impurity). When the Temple in Jerusalem was standing and the laws of tumah were practiced, then housekeeping and cooking became more complicated since a niddah could pass her tumah to people, utensils and food. However, in our day without the Temple we can no longer observe the tumah laws. Therefore a woman may perform her usual household duties while niddah.
Certain specific tasks – serving food to her husband, preparing his bed, and bringing him water to wash – are considered inherently affectionate and are not performed in their usual manner while the wife is niddah. Please see Showing Affection for a detailed discussion of the relevant laws.