Aapojyoti

Came across very interesting term Aapojyoti
I remember chanting this word while performing sandhya vandanam.I don't think I ever gave any thought to the word. Today I was going through a document relating to Upanishad Vahini.
what i understans is Apah means water and Jyoti means light or fire. so I thought, may be it is something to do with elements. But, what I read was a bouncer.

"The waters in conjunction with the fire in the stomach become food. In the water that comes down as rain, the “fire” of lightning is inherent. So, whoever is established in the Aapojyothi, or the Splendour of water, is aware of the Splendour of Annam and is persuaded to revere it."

Water with fire become food.
Rain has lightening inherent in it.
Becoming aware of splendor of water which is splendor of food.

Don't know what does it mean. vedic seer who were talking of philosophy, which went beyond the perception of a lay man and often talked of realm which was beyond mind. They talking of a simple aspect such as food is important looks very puzzling. This is understood by a lay man nay all creature. This compels me to think that food in this context is not simply mean nutritious food, we partake. Water simply does not mean water we see chemically. Light is not just a form of energy what physic has taught to us. It may mean something which says that food is beyond the comprehension of the nutrition science, water beyond chemical science and the energy of fire beyond the realm of physical science.

it gives some respite to know what it does not mean, but that does not quell the thirst as it does not say what does it mean.