Put simply, rain sensors sense rain. They are not a standard component of the backyard irrigation system, but they’re easy to find and are rather beneficial supplements to the basic sprinkler system supply list. A rain sensor for a sprinkler system can help you avoid wasting water.
When coupled with your yard’s irrigation system, they add a layer of automated control to the timeline of waterings. A rain sensor shuts off your lawn irrigation system during significant periods of rain.
It is a relatively cheap device that can save up to 45% of your water bills, help protect the environment, and conserve water.
How a Rain Sensor Works
When it comes to sprinkler rain sensors, there are three primary ways the technology works. The first is by using a collection cup where rainwater is collected and weighed. The weight of the rainwater in the collection cup will then break the electrical connection to the pump or sprinkler valves of your lawn irrigation system.
This same technology will keep the system from turning on at its regularly-scheduled time if there has been sufficient rain recently. Some devices are able to monitor the amount of evaporation that occurs over the next few days, keeping the system off until it’s needed.
The second way is a variation of the first where instead of weighing the amount of water in the collection cup, an electrode is used to measure the amount of rainwater and turn off the system accordingly.
The third way is by using an expansion disc made of cork. When enough rain hits the cork, it expands and triggers the break mechanism of the rain sensor, preventing electricity from running into your lawn irrigation system.
Advantages of Using an Irrigation Rain Sensor
1. Conserve Water
There’s no need to water the lawn when it’s already raining—that’s just wasteful. But traditional irrigation systems follow set schedules without regard for weather conditions.
Adding a sprinkler rain sensor to the mix results in using significantly less water since you’ll be cutting out all the water that was being used during times of precipitation.
If you’re wondering whether a sprinkler rain sensor is worth it, the answer is an unequivocal yes! In fact, in some areas, they are required with the installation of underground sprinkler systems.
Since you typically pay for every drop of water one way or another, saving drops means saving cash. You’ll also pay less for electricity because of the decrease in time the sprinkler system is running.
2. Prevent Disease Damage and Nutrient Loss
All things being equal, plants thrive best with the proper amount of water—not too much and not too little. But if you’re watering on top of nature’s contribution, you’re likely overwatering your lawn and plants.
Grass doesn’t do well with overwatering. It becomes dependent on the water, keeping its roots close to the surface. Healthy lawns dig roots deep into the ground in search of water and nutrients, but that only happens when it feels a bit stressed for water.
Creating gaps in your watering schedule benefits grass for this reason. Oversaturating your lawn or providing light watering too often causes more problems than it solves.
Overwatering can also wash away essential nutrients your plants have not yet absorbed, literally taking food away from them.
Implementing a sprinkler rain sensor helps prevent overwatering, resulting in a nutrient-rich lawn that is more resistant to disease.
In addition to the lawn, your plants will also thank you for not overwatering them. Some plants are very finicky about having wet feet.
Too much moisture can breed bacterial and fungal infections that spread disease in plants. Root rot is a primary problem for plants that can be avoided with proper watering practices aided by rain sensors.
3. Save Money on Fertilizer
Along with the nutrients that get washed away as a result of overwatering, fertilizer and compost are in the mix. It’s a costly endeavor to continuously replace the materials you’re providing your garden just to watch them get washed away again.
A rain sensor prevents you from overwatering your plants and lawn, and therefore helps you avoid the additional time, money, and effort involved in adding more fertilizers and compost to your plants.
4. Increase the Lifespan of Your Irrigation System
The more you use your irrigation system, the more opportunity there is for timers, sprinkler heads, and other components to break and need repair.
Using a rain sensor prevents unnecessary wear and tear on your lawn irrigation system since it minimizes the amount of time that your lawn irrigation is in operation.
Less use can equal a longer lifespan for each piece of your irrigation system.
5. Prevent Groundwater and Waterways Pollution
When excess water hits the ground and cannot be absorbed, it needs someplace to go. This might mean drifting off to a drain field, pooling in the yard, or running out the French drain.
Regardless of the how, lawn and garden runoff is loaded with toxic surface ingredients. A lawn irrigation system equipped with a rain sensor minimizes wasteful runoff such as pesticides, motor oil, fertilizer, pet waste, and sediments from reaching your waterways.
It also minimizes garden pollutants such as herbicides and fertilizers from getting into your groundwater system.
Disadvantages of Using an Irrigation Rain Sensor
Although the advantages of using a sprinkler rain sensor are obvious and measurable, there are some disadvantages to consider.
First, it’s a component that comes with an initial cash outlay. Although you’ll earn your money back through cost savings, it’s sometimes hard to make the investment.
Second, an ill-placed, or incorrectly placed sensor won’t do its job, costing you money with no visible reward.
Third, communication between the sprinkler system control unit and the rain sensor can be inconsistent, especially with wireless models.
Finally—and not really a disadvantage but more of a note—rain sensors are probably not worthwhile in regions with very little rainfall.
How to Install a Sprinkler Rain Sensor
A rain sensor is mounted outdoors away from trees and roof overhangs so that it can collect rainwater without obstruction. A rain sensor can either be wired or wirelessly attached to a lawn irrigation system.
Wired Rain Sensor Installation
Step 1 - Install Wiring
Open the panel to your sprinkler system controller unit. Inside you’ll see a jumper wire that is plugged into wire imports labeled ‘RS’ or ‘Sen’ or something similar that indicates it is meant for rain sensors.
Remove the jumper wires and replace them with the wires from the rain sensor—one in each port. It doesn’t matter which wire you attach first.
Step 2 - Test the System
Once plugged in, the wired system is ready to work. Close the front of the system controller unit and check the spot on the screen that references the rain sensor. It should appear to be on/connected.
To test it, turn the sprinkler system on. Then push the button on the rain sensor to manually engage it. The sprinkler should turn off in response.
Step 3 - Bury the Wire and Place the Sensor
The proper location is crucial to the success of your irrigation rain sensor. Ensure the location is void of any type of covering, including roof overhang or tree branches.
Obviously it will also need to be close enough to the system controller that the cords will reach between the unit and the box. Bury the wire so it is not a tripping hazard. This will also protect it from weatherization and the blades of the lawn mower.
Depending on the layout of your house, yard, and control unit, you may also be able to run the rain sensor unto the roof, which will allow it to function appropriately without the need for burying the wires.
Wireless Rain Sensor Installation
Wireless systems transfer signals electronically so there’s no need for a direct wire connection.
These systems provide much more flexibility when it comes to location, since the sensor can be placed anywhere the signal can reach it—typically up to 500 feet away from the control box.
The system is easier to install since you don’t need to bury wires.
Step 1 - Plug in Wires
The wires insert into the same holes in the same manner as for a wired unit. However, the wires go to a receiver unit rather than directly to the rain sensor.
Safety Note: Turn off power to the controller before doing any wiring.
Step 2 - Mount the Receiver Unit
Mount the receiver unit in a location near the sprinkler system control box. It will simply screw into the house, fencing material, or other location.
Once power is restored, both the receiver unit and the controller unit should show the rain sensor is active. Make sure to check the procedure for your particular model. You may need to initiate the active status.
Step 3 - Mount your Rain Sensor Unit
Choose a location for your rain sensor that is void of overhang and mount the unit to a post, side of the house, roof, or other suitable location.
Step 4 - Sync the Devices
Finally, you’ll want to follow your rain sensor model’s instructions for syncing the receiving unit to the rain sensor.
Rain Sensor Features
Although very basic in design, the technology offers a range of features to consider. The least expensive models will simply work within the parameters of predetermined factory settings.
Other models allow you to customize the response of the unit. For example, you can adjust the rain sensitivity so the rain sensor doesn’t turn off if it’s misting out. Perhaps you want it to collect a measurable amount, such as ¼” before overriding the system.
The same is true in reverse. You may want to make your sprinkler rain sensor more sensitive by setting it to respond to very light rain.
You can also set it to override the sprinklers based on the temperature, even if it’s not raining at the time. These features allow owners to tailor the system in response to the unique needs of individual yards.
How Much Do Rain Sensors Cost?
Like most products, irrigation rain sensors come in a variety of price points. You can source a basic model for as low as around $25. At the top of the price range, rain sensors can run around $200.
Either way, you’re going to get your money back in water cost savings, particularly if you live in a rainy area, or experience tropical-type afternoon downpours.
Some of the top brands of rain sensor to look for are Toro, Irritrol, Rain Bird, and Hunter.
Like other components of your sprinkler system, rain sensors will wear out and malfunction too. If your sprinkler rain sensor isn’t working, check the wiring to ensure there’s no damage or disconnect.
For wireless systems, check the wireless connection to see if it’s the source of the problem.
You may also have a dead battery inside the rain sensor on wireless-type units.
If all indications point to replacement, think about how long you’ve had your unit. Most sprinkler rain sensors have an expected lifespan of around three to five years.
After reading through the many advantages of implementing a sprinkler rain sensor, it’s easy to see it’s a beneficial addition to the irrigation system, the landscaping, the environment, and your wallet.
Of course, if you don’t already have an underground sprinkler system, the project is much larger than if you’re simply adding a rain sensor to an existing irrigation system.