How to Find The Precipitation Rate For Your Sprinklers

Knowing each zones precipitation rate for your sprinkler system is crucial for setting a proper watering time. It will allow you to make sure your plants get all the water they need while not going over your soil’s infiltration rate. When that happens you get water run off and waste.

There are many ways to do this and a helpful chart to follow. You’ll have to find out a few things about the zone you want to start with first. It’s important to know that every zone must be done separately.

You’ll have to look find at least one full spraying head, meaning 360° spraying. The nozzle should show a GPM (Gallons Per Minute) on there. If it doesn’t but shows the brand and model, you can look up that nozzle chart online. Otherwise, you’ll have to do it manually by using the formulas. You’ll also have to find the spacing between each head in feet.

Ideally, they all your nozzles are the same brand. This is how we get a matched precipitation rate. So, every nozzle distributes a proportional amount of water in comparison to each other.

Spray head nozzles match themselves if they are all from the same manufacturer. With rotor heads, you must match them manually. So, if you have a 6.0-gallon nozzle on a 360° head. To match your precipitation rate, you must put a 3.0-gallon nozzle anywhere you are only spraying 180°, and a 1.5-gallon nozzle spraying 90°. This is matched precipitation.

You can also get the GPM by watching the water meter while running that zone. Once you know your GPM for that zone, we also need to know how far apart the heads are from each other on that zone. Then line up your answers on the chart to find your PR (Precipitation Rate).

You can find your Precipitation Rate using the chart or manually using these different formulas.

Total Area Method for Precipitation Rate:

One of the preferred methods because it accounts for all heads at once. You can get this number by watching your water meter or a flow meter.

Precipitation Rate = 96.3 X Total GPM/ Total Area Covered by That Zone

(GPM – Gallons Per Minute)

Specific Area Method for Precipitation Rate:

Popular for calculating one zone at a time.

Precipitation Rate = 96.3 X GPM (Of one 360° head) / Head Spacing X Row Spacing

(GPM – Gallons Per Minute)

Triangular Spacing Method for Precipitation Rate:

For heads spaced in a triangular spacing fashion.

Precipitation Rate = 96.3 X GPM (Of one 360° head) / (head spacing)2 X 0.866

(GPM – Gallons Per Minute)

Maximum Safe Flow in GPM for Sizing Pipe

Understanding the maximum safe flow for various pipe sizes and materials is crucial for efficient irrigation system design.

This chart outlines the gallons per minute (GPM) capacity for different pipe types, including Class 200, Class 315, Schedule 40, and Type K Copper, across common pipe sizes. Selecting the correct pipe size ensures optimal water flow while avoiding issues like pressure loss or system inefficiencies.

Use this chart as a guide to match your water flow requirements with the appropriate pipe type and size. For more advanced irrigation needs, additional pipe sizing charts and guidelines are available to help you make informed decisions about stepping down to smaller pipe sizes when necessary.

How to Use the Chart

1. Identify Your System’s Flow Rate: Begin by calculating your system’s total flow rate in gallons per minute (GPM). This value is based on the water output of all sprinklers, emitters, or other irrigation devices in the zone.
2. Select the Pipe Type: Match your pipe material with the chart columns:
   • Class 200: Lightweight, economical pipe with moderate pressure tolerance.
   • Class 315: Stronger PVC option for systems needing higher durability.
   • Schedule 40: Thicker walls and suitable for higher-pressure applications.
   • Type K Copper: Heavy-duty pipe with excellent longevity, typically used in specialized applications.
3. Locate the Safe Flow for Your Pipe Size: Find your required GPM value in the column for your pipe material. Move across to determine the correct pipe diameter. For example:
   • If your system requires 12 GPM and you’re using Class 200 PVC, a 1-inch pipe would safely accommodate this flow rate.
4. Account for Length and Pressure Loss: Longer pipe runs increase friction loss, which affects water pressure. For extended runs or systems with significant elevation changes, consider upsizing your pipe to minimize pressure loss.

FAQs About Sizing Pipes with the Chart

1. What happens if I exceed the maximum safe flow for a pipe size?
Exceeding the recommended flow rate increases friction, which can cause water hammer, pipe failure, or uneven distribution of water across the irrigation system.

2. Can I use this chart for all irrigation systems?
Yes, but it’s essential to combine this data with site-specific considerations such as pipe length, elevation changes, and system pressure requirements. For highly complex systems, consult an irrigation specialist.

3. What is the difference between Schedule 40 and Class 200 pipes?
Schedule 40 pipes have thicker walls and higher pressure tolerance compared to Class 200 pipes. They’re ideal for systems with high water pressure or longer pipe runs, while Class 200 pipes are suitable for more standard applications.

4. How do I calculate my system’s total GPM?
Add the GPM output of all sprinklers, emitters, or other devices running simultaneously in the zone. For example, if you have 10 sprinkler heads, each using 1.5 GPM, your total system flow is 15 GPM.

5. Do I need to upsize my pipe for long runs?
Yes, long pipe runs result in friction loss, reducing water pressure at the farthest points. Upsizing the pipe compensates for this loss and ensures consistent performance across the system.

Tips for Pipe Sizing Success

• Understand Friction Loss: Friction loss increases with pipe length and flow rate. Use this chart as a starting point, but adjust for friction loss using additional resources or software.
• Match Materials Consistently: Mixing different pipe types (e.g., Class 200 PVC and Schedule 40) can lead to uneven performance and maintenance challenges.
• Plan for Future Expansion: If you anticipate expanding your irrigation system, select pipe sizes that can handle the increased flow rates without the need for costly replacements.

By understanding and applying the Maximum Safe Flow in GPM for Sizing Pipe chart, you can design an irrigation system that balances efficiency, durability, and cost. Proper pipe sizing ensures smooth operation, minimizes repairs, and delivers water exactly where it’s needed. For more detailed guidance or specific questions about your system, consult a professional irrigation specialist here at Lawn Sense.

Chart of Average Historic Rainfall in Texas 

Understanding the historic rainfall patterns in Texas is crucial for homeowners, landscapers, and irrigation professionals. This chart provides the average monthly rainfall in inches for various cities across the state. By referencing this data, you can make informed decisions about watering schedules, irrigation setup, and plant choices.

How to Use This Chart

1. Determine Your City’s Averages: Locate your city in the chart to understand the typical monthly rainfall patterns. For example, if you live in Houston, you’ll notice that June tends to have the highest rainfall at 5.25 inches, while February averages only 3.5 inches.
2. Plan Your Watering Schedule: Use the chart to identify months with lower rainfall and adjust your watering schedule accordingly. For example, in dryer months like August or January, your lawn or garden may require more supplemental watering.
3. Set Up Smart Irrigation Systems: If you have a smart irrigation system, like a Hydrawise timer, this chart can help you program predictive watering settings. Such systems can sync with local weather stations and automatically adjust based on rainfall trends.
4. Monitor Seasonal Trends: Compare the summer weekly averages to the rest of the year. Summer often requires careful monitoring of irrigation due to higher temperatures and faster evaporation rates.

FAQs About the Historic Rainfall Chart

1. Why is this chart important for irrigation planning?
The chart provides average rainfall data, which helps you estimate how much supplemental water your lawn, garden, or crops may need. Proper planning reduces water waste and keeps plants healthy.

2. Can I rely solely on this chart for watering?
While the chart is a great baseline, it’s important to also account for current weather conditions, soil moisture levels, and plant needs. Pair this chart with a rain sensor or weather station for the best results.

3. Why is there such a variation in rainfall between cities?
Texas is geographically diverse, with coastal areas receiving significantly more rain than inland or desert regions. For instance, Houston averages over 49 inches annually, while El Paso sees just 7.10 inches.

4. Does this chart account for future rainfall patterns?
No, this chart provides historic averages and cannot predict future rain events. However, it’s still a valuable tool for understanding long-term trends and planning accordingly.

5. How do I adjust for sudden changes in rainfall?
Consider using a rain sensor or manually turning off your irrigation system when there’s unexpected rainfall. Smart irrigation systems can also help manage this automatically.

Historic Average ET Rates (Evapotranspiration)

Evapotranspiration (ET) is a critical measure for understanding how much water your plants, lawn, or crops need. ET combines the evaporation of water from the soil and the transpiration from plant surfaces to calculate the total water loss. This chart provides the historic average ET rates for cities across Texas, giving you a reliable starting point for managing irrigation effectively.

How to Use This Chart

1. Identify Your City’s ET Rates: Locate your city in the chart to see how much water your plants typically lose each month. For instance, in Austin, ET rates peak at 8.12 inches in July, while the lowest rates occur in January at 2.20 inches.
2. Match Watering to ET Rates: Use the chart to determine how much water to replace during different months. If your city’s ET rate is 6 inches in a summer month, your irrigation system should provide approximately that amount of water to keep your plants healthy.
3. Optimize Irrigation Systems: Combine this data with smart irrigation technologies. Many systems allow you to input ET rates to ensure precise watering based on plant needs and seasonal conditions.
4. Plan for Seasonal Variability: Higher ET rates in summer indicate the need for increased watering, while lower rates in winter reduce irrigation requirements. Adjust your schedule accordingly to save water and promote plant health.

FAQs About the Historic ET Rates Chart

1. Why is ET important for irrigation planning?
ET rates help determine the actual water demand of plants by accounting for water lost through evaporation and transpiration. This ensures efficient water usage and prevents overwatering or underwatering.

2. How do I calculate how much water my lawn needs using ET?
Take the monthly ET rate (in inches) for your city and divide it by your irrigation system’s efficiency. For example, if your system is 75% efficient and the ET rate is 6 inches, you’ll need to apply 8 inches of water (6 ÷ 0.75).

3. Can I rely solely on this chart to determine watering needs?
While the chart provides a solid baseline, you should also consider real-time weather, soil moisture, and plant types. Pairing the chart with a weather-based irrigation controller will yield the best results.

4. Why do ET rates vary so much across Texas?
Texas has diverse climates, from humid coastal regions to arid desert areas. For example, Galveston’s ET rates are lower due to higher humidity, while El Paso’s rates are higher because of its dry, arid conditions.

5. Does the chart account for irrigation system efficiency?
No, the chart only shows raw ET data. You’ll need to factor in the efficiency of your irrigation system when calculating water requirements.

Tips for Using ET Data Effectively

• Combine ET Data with Rainfall Information: If you’re also using the historic rainfall chart, subtract the average rainfall from the ET rate to determine how much supplemental irrigation is needed.
• Monitor Seasonal Trends: ET rates peak during the summer when temperatures are highest. Be prepared to increase watering during this time while ensuring it aligns with any watering restrictions in your area.
• Invest in Sensors: Soil moisture sensors and weather-based controllers can use ET data to automatically adjust your irrigation schedule, maximizing efficiency.

Are you someone who takes your lawn’s health seriously? If so, chances are you use your sprinkler system regularly. If you’re a DIY’er you’ll want to check out this tip for replacing a sprinkler head without digging. Consistent use of your system is necessary for a variety of reasons, which we’ll get into in another post. But in short, sprinkler systems not only keep your lawn healthy but will keep your foundation secure as well. Like anything else regular use means regular maintenance. In time a number of things will go wrong, some will be easy and some will be more difficult. This is one of the easier DIY sprinkler repairs for your sprinkler system.

The easiest way to replace a sprinkler head is to do it without digging. There are a number of other articles out there on the subject. The difference with our blog is it’s written by experienced sprinkler technicians who actively work on sprinkler systems, not by career bloggers.

Materials Needed:

• Exact model of the sprinkler head you want to replace.
• Small shovel (Can be done without).
• Small channel lock pliers (Can be done without).

#1 – Locate the make and model

To locate the make and model of the sprinkler head you are trying to replace follow these simple instructions.

• Clear grass and dirt from around the top cap of the head.
• Unscrew the cap to the left, using the pliers if necessary. (See image below)
• Remove the cap and internals. It will look like a big spring.
• Make sure the body of the head stays in the ground.
• Rinse off the cap so you can see the make and model.
• Try to keep dirt from falling in the body.

If you’re specific head isn’t available for purchase or the threads on the body are damaged you won’t be able to replace a sprinkler head without digging. You’ll have to replace the whole head. For help with that you can read about it here.

Don’t forget!

Remember to check the nozzle for size and GPM info if you can’t or don’t want to use the old one. This way you can get the correct new nozzle for the new head. You can read more about which nozzle to buy here.

#2 – Screw on the new cap

Once you have your replacement head the process is just as simple as the first.

• Unscrew the cap from the new head
• Don’t install the nozzle just yet.
• Screw the new cap onto the old body in the ground hand tight.

#3 – Final steps

You’re probably wondering why the nozzle isn’t on yet. Anytime you change sprinkler heads even without digging or when doing other repairs where dirt can get in the lines you’ll need to flush the system. Sometimes it’ll be necessary more than once. To do this turn on the zone with the new head without the nozzle. Once the water comes on immediately turn it back off once you see water shoot in the air.

Now that head is flushed. Now you can install the new nozzle. It can be adjusted with the zone on or off. You can read more about adjusting nozzles here.

• Sprinkler Repair
• Fertilization & Weed Control
• Outdoor Lighting

What To Do If Your Sprinklers Won’t Turn Off – How to Fix

Almost every day we get calls from frantic homeowners who wake up and see their sprinklers running when they aren’t supposed to be. Confused, they go to the timer in the garage and turn the switch to off. They are surprised to see the sprinklers still running. With money literally washing down the street you need to act quickly. This guide will show you how to shut off sprinklers that won’t turn off without shutting off water to your home.

This blog is written by licensed professionals in the Dallas metroplex. These tips are based off of what we see in the field for our area.

Materials Needed:

Handling sprinklers that won’t turn off is a job that can be done without any tools if your backflow device is visible and in good condition. If not, these tools may be necessary.

• Shovel possibly
• Pliers possibly
• Hand water pump possibly

Find the backflow box

The first step to fixing sprinklers that won’t shut off is knowing what type of backflow device you have. You can read more about backflow types and what they are used for here.

Generally in a regular neighborhood lot you’ll have what is called a double check backflow device. These are located in a big rectangular box in the ground. Typically, the box is located within 10′ of the city water meter. It could be on the other side of the sidewalk as well if you have one. In some instances we have seen backflow devices located in the flowerbeds near the house.

If you are having trouble finding the box, it’s probably covered with grass. Once you’ve found it you can move on to the next step. If you still haven’t found it read the next paragraph.

Locating a buried backflow can be a pain but here is how we approach it. We look at your neighbors house and see if we can locate their backflow easily. Chances are yours is in a similar spot. From there use your shovel to poke around in the yard. You’ll want to look first in a similar spot as your neighbors, then all around the water meter within a 10′ radius, lastly in the flowerbeds. When the shovel hits the plastic box you’ll feel it and hear it.

Gain access to your backflow

The next step to handling your sprinklers that won’t shut off is to gain access to the device. With a properly maintained backflow you’ll be able to skip this step. Unless, the box is full of water.

If you open the lid and it’s full of water you can use a hand pump as shown above to pump the water out quickly. You can purchase this tool at Lowe’s or Home Depot. Often, when we open up the lid the backflow is surrounded by mud. You’ll have to clean out around the backflow to gain access to the handles. Ideally, there should be no dirt touching the backflow while it’s in the box. You’re almost ready to fix your sprinklers that won’t turn off.

Turn off the backflow

Now that the backflow is cleared and accessible you’re ready to get your sprinklers turned off. Again, with a properly maintained backflow this step can be easy. When the water is on the handles will be parallel to the pipe. If the water is off the handle will be perpendicular to the pipe. To shut off the backflow turn one of the handles 90 degrees. Now, these handles only turn one direction. If you look at the base of the handle you’ll see metal stoppers that will indicate which way it turns.

Note: Don’t mess with the test ports on the top of the backflow device.

You may experience stuck handles or even missing handles if they are rusted. This is where the pliers come in. Before you use the pliers be sure you are turning the handle in the right direction. If you use pliers grab onto the nut in the middle and turn that instead of the handle.

Now you’re done

Once you have the handle turned fully perpendicular the water should be off. To confirm this make sure the metal stoppers are touching. You should only have to turn off one handle to accomplish this. However, we have seen where one valve doesn’t close all the way letting water pass through. If this happens, turn off the other handle. We recommend replacing your backflow every 10 years as well as regularly cleaning out the box to keep the device from rusting. Yearly testing is also required by most cities which ensures this device still works internally.
If you need help in the Dallas metroplex Lawn Sense can help!

If your sprinklers won’t turn off or you have other issues call us today at (972) 348-0475 or fill out the form on the home page to get scheduled ASAP!

• Sprinkler Backflow Repair
• Fertilization & Weed Control
• Outdoor Lighting

Two Most Common Types of Sprinkler Heads In Your Lawn

This is a blog for DIY homeowners who want to work on their sprinkler system. Written by licensed, field trained technicians in the North Texas area. If you’re wondering what types of sprinkler heads you have or which one to use this will help. Above are the two most common types of sprinkler heads you’ll find in your lawn.

The left head is what we call a “rotor” and the right is called a “spray” head. Rotor type sprinkler heads are typically used for large open sections of grass. Spray type sprinkler heads are used for smaller sections typically. You can use spray heads in large areas or vice versa. Just be sure to have the correct nozzles and spray patterns set.

The nozzle for the rotor type head is the blue piece you see in the picture. This controls how much water is let out only. The nozzle for the spray type head screws to the top of the stem. This nozzle controls water flow as well as the angle at which it sprays. They can be set from 0-360 degrees. To adjust how far out they spray it’s easiest to buy a new nozzle for that distance.

If you’re getting ready to replace one or more of your sprinkler heads, check out our tips.

We always recommend keeping the same type of heads on each zone. Don’t mix and match head types because they each have different precipitation rates. Mixing them up can affect the amount of water being put out, as well as affect the water pressure for the other heads.

If you need help in the Dallas metroplex Lawn Sense can help!

Call us today (972) 348-0475 so we can get you on the schedule ASAP! If we don’t answer or call back in one hour lunch is on us!

• Sprinkler Repair
• Fertilization & Weed Control
• Outdoor Lighting