Tap water has to come from somewhere. Dig a well, dam a river or desal the ocean, they all have significant costs to produce, treat, and distribute the water.

Tap water has to come from somewhere. Dig a well, dam a river or desal the ocean, they all have significant costs to produce, treat, and distribute the water. Even if you did build one of these devices outside your house, you'd still need to pressurize and plumb it into your house's water supply. Simply producing water is but one step among many to make that water usable.