Stir water, kidney beans, corn, crushed tomatoes, lentils, black beans, tomato paste, sugar, chili powder, cumin, and paprika together in a slow cooker.
Cook on High for 6 hours.
Heat olive oil in a large skillet over medium heat. Cook and stir onions and garlic in hot oil until the onion is translucent, about 5 minutes. Stir into the chili.
Continue cooking chili on Low until the beans are completely tender, 4 to 6 hours more.