Sand the side of the seed lightly with fine-grit sand paper until the dark coating gives way to white. As soon as you see any white, stop sanding.
Drop the seed into a clear plastic cup of water. Place it in a spot with temperatures between 70 and 90 degrees Fahrenheit.
Change the water in the cup if it gets cloudy. You may need to change to a clean cup too if scum forms on the inside walls. Clouds and scum are normal. It can take the seed a few days to a few weeks to germinate.
Transplant the germinated seed to a deeper water container if the pond where you'll eventually put it is deeper than the plastic cup. The newly emerged stem grows upward until it reaches air and then unfurls the first leaf. Once they've put out leaves, young plants don't tolerate changes in water depth, so it is important to get the depth measurements correct.
Transplant your seedling to the pond or container before any roots sprout. If you are potting it and then putting it in your pond, ensure the container is round and at least 5 inches deep and 8 inches in diameter. Clay-loam soil works best for lotus plants.