The "scientific" explanations about surface tension and stuff have all been disproven by "real science." The "effects" have been quantified, and are negligible at all impact velocities up to "free fall terminal" speeds.

It still is good advice to "see the surface" in some cases, for experienced people, because the ripples produced by even a small surface disturbance are sufficiently different for very shallow water than for deeper water, so for water less than a very few feet deep you can (but aren't likely to know how to) "read" the depth from the ripples. This won't tell you whether the water is deep enough to dive safely, but can confirm that you're not diving into a mere mud puddle.

In swimming pools, since the sidewalls and bottom are nearly always painted (or tiled) the same color as what you expect to see when the pool is full, it can be hard to tell if there's any water in the pool if there are no ripples, and significant numbers of people are injured (or killed) every year by diving into empty pools where they assumed there was water. In most pools, it's unnecessary to toss a pebble, since the circulation/filtration system will make enough ripples for the surface to be visible. If the pool is "completely flat" it probably means that the filters are shut off, and the pool is still polluted from the last person whose clumsy dive knocked the pee (or poo) out of him/her, so that might be almost as good a reason for not diving as the possibility that the pool is empty.

(See the movie, Caddy Shack, that hilariously dramatized the folk warning that in a public pool you "don't eat the Baby Ruth?")

John