Signal multiplexer or binary zone coding to reduce the number of required signal wires

I used up all my power and signal wires and have new ideas to automate my watering with well pump and house water even more.
To do that I need more wires or multiplex the existing ones.

Did anyone try that? What low power multiplex can be recommended?

I guess for signal wires I need 2 for 24VAC solenoid power supply and 3 to multiplex or binary code the sprinkler zone to run 8 zones.

With now only those 5 wires used I can free up 3 wires for extra gimmicks.

I need the outside circuit to be 100% waterproof and it needs to survive freezing temperatures.

Any suggestions???