I put a 20″ “Big Blue” water filter and all incoming water first go through this filter. The water then branches off in 4 directions each controlled with 1/2″ quarter-turn ball valves.
1 goes to the R/O system
1 goes to the tank fill.
1 goes to the gray water tank
1 goes to the black water tank.
Each valve is color-coded.
So, I only have one water hook up and can easily control where I want it to go. And all the water goes through a 5-micron charcoal filter. I also put a faucet at the filter intake, so, I can release pressure before removing the intake hose and this also allows me a place to hook up an additional hose for washing the car, etc.. without any disconnecting.
Directional valves built in each spray nozzle, so in order for a problem to occur.
1 backflow valve would have to malfunction,
2 ball valves would have to malfunction.
There would have to be a negative pressure.
I used a clear hose between the ball valve and each spray valve, so I can also visually check.