Water Heaters Only, Inc is highly rated, read our customer reviews and learn for your self why we have over , happy customers since !.Discover how tankless instant gas water heaters work. These continuous flow units never run out of water are energy efficient. Here’s how they work.Advantages of an Under Sink Water Heater. Reduced Water Waste With the water heat no more then a few feet from the delivery point, you will not waste water while clearing the pipes of cold water..Having an auxiliary heating system with a water option was a high priority for us. Specially on longer trips in colder regions, a warm shower and warm interior makes a huge difference for you personal comfort..