If your 2006 Montery is like our 2006 Montery the only water filter you have is for the ice maker. It is located in the same compartment as the water pump (a compartment in the pass thru storage bay). For drinking water we installed a GE filter system that includes a spigot you install (ours is next to the kitchen sink). The system is available at Lowes and Home Depot. There are several levels of filters available for the system, some filter just the taste and some remove most all contaminates). Installation of the systems requires connecting a water hose (1/4 inch tube) to the cold water piping under the sink, the 1/4 tube connects to the filter (mounted under the sink), and another tube connects the filter to the faucet. The faucet is mounted to counter top by drilling a hole in the corian (surrounding corian will not be damaged by drilling the hole).
We use the filter that removes mostl of the contaminates. Some campgrounds have their own water wells, might be problem. And when using water from the onboard water tank I don't always feel comfortable with the quality of tha water. I also changed the ice maker filter supplied with the coach, it mainly just filters taste. The same GE filter can be installed in the same position as the original ice maker filter.
Both filters should cost around $100 including the hardware required.
