Once you have mapped out your watering devices, you can compute how much tubing and how many fittings you will need. When laying out the main drip line for each circuit, try to connect emitters directly to the line whenever possible.
Microtubing serves a purpose, but too much can be a nuisance. It snags rakes and tools and is easier to displace or damage.
For drip tubing on a slope, plan to run a main drip line downhill and tee off it with separate horizontal runs of tubing rather than weaving one line across the hillside.
List the number of devices of each type by output and calculate the total output for each circuit. If the total output from your watering devices is much less than the maximum, or if you are using pressure-compensating emitters, the tubing can be longer. If it's over the maximum, change to slower devices or use more than one circuit for the hydrozone.
For a drip circuit that starts farther out than 200 feet from its control valve, lay PVC pipe underground to the irrigation area and run your drip tubing off a riser. Alternatively, run 3/4-inch polyethylene tubing aboveground to the start of the new zone and connect 1/2-inch tubing to it there.
Other Essential Components
To complete your supply list, you'll need several other items. Any drip system needs a backflow preventer. Backflow preventers can be located at the point of connection, along the main irrigation line to the control valves, or in the control valves themselves. As with a sprinkler system, you have a choice of control valves and timers.
Drip systems also require head assemblies, one per circuit. A head assembly always includes a filter and a pressure regulator, and may include a fertilizer injector. You assemble it yourself from separate pieces. Place a head assembly at the hose bibb for a single drip circuit, or just after each control valve on a multicircuit system. If you connect at the hose bibb, use components with hose threads. To connect to a control valve, you'll need components with pipe threads.
Filters
Small, in-line filters are the least expensive and are usually sufficient for small systems and clean water supplies, but you have to take apart the line to wash the screen. Larger Y-filters allow for easier cleaning. 
Pressure regulators
A pressure regulator lowers the household water pressure, which is often too high for a drip system, to a more suitable 15 to 30 psi, protecting the fittings from blowing apart and helping watering devices work properly.
Regulators come in a range of psi ratings. Use 25- to 30-psi regulators for most circuits; 20 psi is better for a circuit starting at the top of a slope, since water gains pressure as it travels downhill. Sprayers and minisprinklers with rotors take a higher pressure than drip emitters do; check the manufacturer's information.
You can also place an adjustable brass pressure regulator at the start of the system, before the valves, although it gives you less control of the individual circuits. If your water pressure is very high (over 80 psi), install a pressure regulator both before the valves, to protect them, and in the head assemblies after each valve.
Fertilizer injectors
Drip irrigation does not work well with traditional methods of fertilizing, which rely on overhead watering to dissolve and spread the fertilizer. Consider installing a fertilizer injector (shown at left), which sends nutrients directly into the plants' water supply.
Tools and supplies
The tools to install a drip system are simple and easy to use. Cut the tubing with a good pair of pruning shears or a utility knife. A specially designed punch (shown at top right) makes holes in tubing for emitters and connectors, and "goof plugs" (shown at right) stop up holes in the wrong spots. Stakes (shown at middle right) hold tubing in place.
Sprinklers & Drip Systems Take the mystery out of installing a watering system with this new edition of Sprinklers & Drip Systems. Visual guides and garden plans help you select, install, and maintain the right system for your landscaping needs.
