On Karva Chauth, married women observe a nirjala vrat (fast without food and water) from sunrise to moonrise. They observe the ritual for the safety and well being of their husbands.
Married women who observe Karva Chauth break the fast only after offering prayers to the moon. Women offer water to the moon as a part of their prayer by holding an Atta Chani in another hand.
Since Karva Chauth or Karwa Chauth is celebrated primarily by women, men are entirely excluded from the festival's observances until moonrise, though they are expected to demonstrate attention and concern for their fasting wives.