it's owned by the landlord.
then you shouldnt concern yourself with fixing it?
or try one of these float valves. http://www.google.com/products/catalog?h...ved=0CGUQ8wIwAA
and connect it to one of these electric valves. http://www.google.com/products/catalog?h...ved=0CF8Q8wIwAQ
then you wont be buying the heater elements everytime you forget to fill the tank.
BTW , you can build a tank outside the water heater tank and use the float valve inside it.
the water levels should be the same in each tank if you position the external tank correctly.
just remember to flow water from the bottom of the external tank to the bottom of your water heater so that the water levels can equalize.
and if you have a pressurized water heater tank then make sure you use a pressure external tank.
just use an old salvage yard electric water heater , remove the heating element and build a fitting that allows you to insert the float into the hole for the heating element.
this way you wont be invading your landlords property only adding a appliance.
I have never seen a water heater that required manual filling
so Im not sure exactly what you have , but maybe the above will give you an idea or two on how to repair this neglect.
could it be that when you moved into the property the landlord had turned off the water valve leading to the water heater because the property was vacant?
have you tried to just leave the water valve on?
you may have a pressure vessel for a water heater tank so if you leave the water valve on the water pressure will equalize and the water will stop entering the tank until you use the hot water again.
is this the type you have?
if so maybe you can just disconnect it and put several of these together for much better hot water at a much better price than all of the above.
Caution: the above solar hot water heater ( garden hose ) delivers extremely hot water.