Have water in resonator and have to refill every.

The purpose for the coolant reservoir is for expansion, when at operating temperature the water expands and have some go into the reservoir, When the engine cools coolant /water condenses and draws the fluid back in, in you case you are loosing it, this is mainly due to a leak, means you need a pressure test to find the leak. This can be at a number of places, the waterpump, radiator, heatercore, cooling hoses

As he said, get a pressure tester from the local parts store and when the engine is cold, pressure test the system. Once it is pressurized, then you need to look for leaks.