I have come across a few older places lately where the irrigation system is connected to the mains water. What I have found is that there hasn’t been a Retic Kit or a non-return valve used.
In this photo is an example for what it should look like from your main water connection to the master solenoid.
The reason for having these valves in place is to stop any fertiliser or chemicals that you are using; in or around your garden area finding its way back into your main water supply to the house.
Something to keep an eye out for…