Mama Cando you might want to look at a instant hotater heater they are way more efficient than a tank. We use a brand called takagi they are expensive but over time they save on fuel just make sure water to them.is not hard as it messes with heating elements.
If you do have hard water getting a filter helps but ask as there is a cheap version and a more expensive the more expensive uses way less salt and pays for itself.
Also before the water intake to heater make a van der waal feild with magnets it increases the absorbtion of water and keeps any particulate suspended. You make them by buying 4 neomolydium magnets about half the size of a pencil a ranging the so all the poles align so all north on way all south another it means they all push apart. Then at the 4 compass points touching the inlet pipe tape them on using duct tape. These magnets will not last forever as condensation will erode them but will last for a decade.