There is only one water lily that is called lotus and that is the Egyptian Blue Lotus (Nymphaea caerulea). I believe, if I'm correct with this, that there are some water lilies that are crosses with lotus which I thing the class or family or something is called lotos but mainly, water lilies and lotus are different.

Cross usage of the common name lotus is part of the problem, as are ebay sellers using lotus and lily in the same description just to get keywords in.

But lotus and waterlilies are distinct types of plants with lotus in the genus Nelumbo (family Nelumbonaceae )and waterlilies in the genus Nymphaea (family Nymphaceae )

To my knowledge there have been no crosses between lotus and lilies; Lotos is a subgenus in the waterlily family that groups together most of the night blooming waterlilies and in no way involves Lotus.