They will come knocking on your door and offer to replace your existing water tank at no cost but you will have to sign a 15 year contract to rent one from them.
So let's say the monthly rental cost is $25 multiplied by 15 years (not taking into account inflation) = $4500 for a water tank that you do not own!
Alternatively, Home depot and Lowes have sales going on right now in which you can get a tank for $500-$1200 including installation. The great thing is that you OWN the tank and if it ever breaks down, you could always purchase a new one or two and it will still cost less than if you signed a contract with this company.