Do your research before putting anything in your eyes. YouTube is a good place to start as you will be able to see and hear personal stories of those who have done it. My suggestion is to do this for your health and you might get a nice side effect of lighter eyes. Do let us know your results. Firehoses and water saws would be some of the more extreme versions, as would looking upward into Texas hailstorms or taking a close peek at the output of a boiling teapot. Reining in to low velocity room temperature liquid water that is reasonably free of unbalanced pH, toxins, pathogens, and the like, the central issue will then move over to the difference between pure water and tears, the stuff your eye is used to. It’s never pleasant opening your eyes underwater, even if the water is not saturated with swimming pool chlorine and is, by and large, clean. Tears are salty, and aside from salt, also contain other body-secreted substances to help reduce drying, and, very importantly, lubricate the relative movement of the eye in the surrounding socket, and the continuous blinking of the eyelid over the eye. Immersion to or exposure to plain old water will dilute or wash away those extra ingredients, and, as most of us have likely encountered in some period of playing in a swimming pool, the longer you keep em open, the rougher and gnarlier your eyelids start to feel after you’ve stopped.
I’m not going to claim an ophthalmologists training on what a threshold is in this case, but consider the volumes for pharmaceuticals like eye-wetting drops, OTC or prescription. The body really does not respond well to inflammation, and open eyeball in not-tears liquid goes that direction quickly. A moment or two is not likely to do any lasting damage, at least by my life experience, (though I suppose it’d be something to try to blame a cataract on rather than genetic inheritance from grandma, but, as I said, I’m not that kind of doctor). Secret spaces behind waterfalls in the Kakadu; or Byzantine mosaics and churches being quietly, privately excavated under travel agencies in Istanbul; or places where you can see real stars over a big city or from the top of a skyscraper or a mountain. Bonus points if you own the plane and land rover and the property & have champagne in a picnic basket in the boot. Extra bonus points if you/your family gave the property up for a community/state/national park. There is nothing like a kiss in the rain; or hike up a mountain with an amazing romantic view; or having a passion and confidence and comfort in who you are, what you do, and what you want.