I'm in the process of changing out the fresh water plumbing in the engine room from the water tank connection (at the engine room fwd bulkhead).
I'm going to include a std 10" carbon filter for the entire boat (to protect the RO membranes and provide better water for consumption), then a ball valve to shut off fresh water to the watermaker, then plumbing into the watermaker prefilter and the auto flush valve.
The reason for all this, is I had a problem with the 3-way valve leaking to the seawater circuit, which others have experienced. If you have this problem, and you have the seachest thru-hull valve closed, you could fill the generator with fresh water. (note that Apolo has a warning on their 3-way valve that if the pressure on the closed side is higher than the pressure on the open side, the ball may unseat and leak to the low pressure side). I had this happen when we were out of the water with the seacock closed, in a boatyard for 3 months.
To prevent this serious problem I'm adding a ball valve prior to the 3-way valve. Since I'm replacing the water pump and eliminating the surge tank, I have room for the carbon filter and new stainless plumbing. If anyone is interested I'll post a photo when I'm done.