Why Filter CID Water?

Water filtration is important for all irrigation systems. As you probably know, CID takes water from the Yakima River. Runoff from the Cascade Range carries all sorts of debris down the river.  From March to June you are more likely to have silt or sand, small sticks, leaves, decayed animal parts, clam shells and murky water delivered to your service riser.   From June to October the river changes; it runs slower, is shallow and becomes a breeding bed for aquatic weeds and algae.

While sand is probably the first thing most people think needs to be filtered out of the water, organic materials can be just as important to remove. Algae can grow inside the system, especially in drip tubes. Another situation occurs when a small piece of organic matter snags somewhere in a valve, fitting, emitter, or sprinkler. The organic matter by itself may not be large enough to be a problem. But soon another piece comes along and gets caught in the first. Then a very small grain of sand that would normally have passed through the system without problems becomes caught in the organic matter. Soon a large build-up of crud forms and the flow is blocked.

Using a filter can help extend the life and lower the maintenance on your sprinkler system. For drip systems they are a necessity to prevent emitters from becoming plugged. Even if small sand particles can pass through your system without clogging it they cause wear on the equipment. Automatic valves contain very small water passageways in them which can become plugged resulting in the valve failing to either open or close. A small grain of sand caught in a spray nozzle can result in a dry, dead spot in a lawn.

 Filter Recommendations

So which filter to use? There is no fixed answer. Your budget, water quality, and availability of the filter and parts must all be considered.

Screen filters are generally the least expensive. The larger bodied filters provide extended filter cleaning durations.  (Illustration 1) shows body size differences between 1 inch, 1 ½ inch and 2 inch screen filters.  Filter screens are sized by the throat diameter at the inlet and outlet ports (Illustrations 2, 3 & 4).   Typically, the larger the inlet and outlet port diameter, the larger diameter and length the filter body will be.






(Illustration 1)
– (From left to right) are 1”, 1 ½ “and 2” screen filters. Notice the screen diameter difference between the 1” and 2” filters. Larger screens will provide you longer durations between flushing’s.







Illustration 2
1” Filter Body and Gray 800 Micron Screen








Illustration 3 1½ “Filter Body and Gray 800 Micron Screen








Illustration 4 2” Filter Body and 500 Micron Screen

Sometimes a combination of two filter helps protect equipment, more than one type of filter will be needed. (Illustration 5) shows how a two-filter system looks. In this illustration, water flows from left to right; the larger filter is 800 microns (stops larger particles), while the second is a disk filter 100 microns (stops small particles such as sand).






Illustration 5 – (left to right) the 1 ½ “filter screens out larger particles; the smaller filter screens to collect sand and fine grit.
How much Filtration do you need?

What’s the smallest size of particle that needs to be removed from the water by the filter? The amount of filtration you need is dependent to a large degree on what type of irrigation you have. For example, drip irrigation systems need a much higher degree of filtration in order to protect the emitters from plugging. For most applications the amount of filtration is measured by the “mesh size” of the screen or maximum size in “microns” of an object that can pass through the filter. There is a mesh vs. micron conversion table at the bottom of this page.

You always want to use the highest level of filtration that is practical. Even if your sprinkler system can easily handle a fairly good size grain of sand without clogging, removing that sand grain is still advantageous as it will eliminate the wear on the system caused by the sand grain as it passes through. The balancing factor is that the more particles removed the more often the filter clogs up and needs to be flushed. Excessive flushing can waste water and energy, so a tradeoff is necessary.  Also, be aware of where your flushed water is going!  Flushing sometimes can cause damage to personal property and erode earth.

Rule of Thumb Guidelines

Drip Systems:

The drip emitter manufacturer will specify in their literature the level of filtration required. I almost always take it one level greater. (That is, I remove even smaller particles than they recommend.) I generally never use anything less than 100 mesh or 150 micron.

Sprinkler Systems:

A 20 mesh (800 micron) filter will remove most particles capable of plugging a sprinkler nozzle, however, I like to use a 30 mesh (500 micron) in order to also remove the particles that can cause wear on the system and damage the valves.

All Irrigation Systems:

Bottom line- I would suggest using at least an 800 mesh (20 micron) screen or equivalent in the filter. I suggest you run the water through a filter before it reaches the control valves. Small grains of sand are one of the most common causes of control valve failure, especially when using the standard electric solenoid valves used on most irrigation systems. My experience is that the savings in valve repairs will pay for the cost of the filter over the next 5 years. With a cost benefit like that it is pretty hard to argue against installing a filter!

Approximate Filter Size Equivalents 




















































Note: Screens are color coded for easy identification of particle size.

The values in the table above are rough equivalents. While the Micron is a standard metric measurement, the term Mesh is rather subjective, especially for values over 300. For example, I’ve seen both 500 mesh and 700 mesh screens that have equal filtration, that is, they both filter out particles down to 30 microns in size. The problem is related to the size of wire from which the screen is manufactured. The mesh designation is based on the number of wires in one linear inch of the screen. So two screens can have the same mesh, but if one is made with thicker wire than the other, the one with thicker wire will have smaller openings between the wires. Therefore, micron is a much more accurate measurement for use in determining the size of particle that can (or can’t!) pass through a filter.