Question

Water in swimming pool or water tank appeas shallower than its depth. Why?

Answer 1

It is due to the refraction of light. As ray of light pass from water to air i.e. from denser medium to rarer medium it bends away from the normal this is called refraction of light.
So when light ray passes from bottom of the pool and reaches our eye it bends away from the normal and its base appears raised.