I found and copied this website for you about the differences between them.
www.abc.net.au/gardening/stories/s1599802.htm
Most gardeners are familiar with water lilies, from Monet’s paintings of the water lilies grown in his remarkable garden in Giverny. They're part of the western tradition of gardening but lotuses are entirely different. We're familiar with them from Chinese paintings.
Most people think of them as tropical plants, but in fact both water lilies and lotuses grow as far south as Victoria. They thrive in small garden ponds, pots and containers, and bring life to a water garden.
Geoff Cochrane has been growing aquatic plants on his property in the Yarra Valley outside Melbourne for the past five years. During that time, he and his partner have managed to collect and successfully cultivate some 150 varieties of water lilies and 200 varieties of lotuses from all over the world.