No really, its quite easy to measure, you have one alkaline no 2 water rice and another filtered water, each to rice cooker with same amount, the one with alkaline water will be definitely softer.
Even with vegetables, you boiled them via A/B test, there is definitely a difference.

True, water is water, the difference is just the alkaline level.

I didn't meant in health, sure body will self regulate it's alkaline level, but for cooking it changes the texture of vegetables for example, and make tea taste smoother.
This is measurable in A/B test, it wasn't that hard to find alkaline water to try it yourself.