You must change fresh water. The zebra finch’s’ primary food is seed. Millet is the principal seed in any finch formula. Properly balanced seed formulas are readily available at pet shops.
Zebra Finches also need a lot of calcium, especially when breeding. Zebra finches love millet sprays. Zebra finches also need a diet supplemented with certain greens like spinach, vegetables and fruits also enjoying a meal of mealworms and other small insects.