If you've planned your project well you know where all the plumbing and electrical will go. Now is the time to get all of this into place.
This is one thing we didn't do very well. We wanted to put in a sprinkler system but got so excited about getting on with our project that we decided to do it later. Well here it is later and we still don't have a sprinkler system. We also want to add path lighting but haven't done that yet. That won't be so hard but still would have been easier before all the paths, ponds and plants were in.
Depending on what part of the country you live in it can affect how you install your water system. If you have freezing weather in the winter be sure and plan for a way to drain or blow out the system. Nothing worse that split pipes that you need to dig up in the spring.
We knew we would be putting in a waterfall, river and pond and would need to get the water from one end of the yard to the other. Here is what we did before we brought in any topsoil or fill.
It's also a good idea to put your electrical into a conduit. Even if it's only a 12 volt system it will protect the wires from being cut when you are digging in the garden later on. The conduit doesn't need to be anything more than a small PVC pipe. You can use bare wire but conduit is better.
If you are going to be building up your yard with fill dirt or top soil you can just lay out your piping on the ground and work up from there. If you aren't filling you will need to do some more digging so get out there and dig!