Our watermaker has a filter on the flush inlet line from our freshwater tank. Hopefully that solves any problems with micro particles of charcoal getting to the watermaker membrane. Besides which the membrane gets seawater pushed past it when it’s being operated so presumably particles of large bit of carbon don’t stick and get flushed away?
The purpose of the 1 micron filter is to protect the carbon filter from sediment out of the tank that would block the carbon filter and reduce its life. Having a 1 micron filter on the water tank is also a great barometer of you water tank condition. If that filter is getting manky then your tank is manky
Yep, change mine annually as well. Mine has had about 15,000 litres through it in 12 months and it was still working fine but the boat has been laid up in a boatyard for 3 months in 35degC temperature. I emptied the tank and refilled. No upset tummy and good tasting water. No chlorination done but we refurbished the tank in 2020 with new WRAS approved paint finish