It might be easy at first to get these two aquatic flowers mixed up, but they have definite distinctions. In fact, though these are both flowers found in water, they actually belong to two separate families of flowers. It is also easy to tell them apart at a glance once you know what to look for.
Simple Expressions writes, "[T]he most commonly cited difference and the one which will help you decide which plant it is from a distance, lies in the leaves of the two plants. The leaves of lotus are emergent, meaning that they rise above the water level whereas the leaves of water-lily are found floating on the water surface. Same is true for their respective flowers; lotus flowers are emergent and water-lily flowers are floating."
Curious about more in-depth differences? This video will answer your questions.