Most drip networks that stop working after two seasons do not die from a burst pipe, they die from blocked drippers. The water path inside a dripper is tiny, and borehole sand, algae from a pond or silt from a river are enough to close it. The head filter is the part that decides how long everything else lasts. Yet it is often picked from a catalogue without looking at where the water comes from. This article explains how to choose a drip irrigation filter for your water source, how to size it, and how to tell when it needs cleaning, for a farm or cooperative in Cameroon, Côte d’Ivoire, Senegal or elsewhere in West and Central Africa.
Why drip systems clog
The B.C. Trickle Irrigation Manual groups the causes of clogging into four families:
- organic matter and algae, which bridge across emitter orifices;
- iron and sulphur bacteria, which produce slimes;
- mineral particles: sand, silt and clay;
- chemical precipitates of calcium, iron, magnesium or manganese.
A filter deals mainly with the first and third. Chemical precipitates are more a matter of water quality and of how fertigation is managed. According to Agriculture Victoria, the water paths of drip emitters measure 500 to 1,000 microns, the smallest of any irrigation equipment. That is why drip needs finer filtration than sprinklers or micro-jets.
The four filter types and what they catch
Screen filter
A mesh of metal, plastic or synthetic cloth traps particles on its surface. Agriculture Victoria says screens are generally used where water quality is average to high. Their strengths: low head loss and a small footprint. UF/IFAS fact sheet AE57 states that a screen filter should be the primary choice when water is pumped from a well and the only problem is mineral particles. It is not enough once organic matter is present.
Disc filter
Stacked grooved rings form a three-dimensional matrix, halfway between a screen and a media filter. Agriculture Victoria credits disc filters with much smaller backflush volumes and a smaller footprint than media filters. On the other hand, they have more moving parts, must be dismantled when clogged, and need an annual inspection.
Media (sand) filter
A tank filled with crushed granite or silica, graded 0.75 to 1.5 mm according to Agriculture Victoria, filters water through its whole depth. It gives the highest degree of filtration and is the usual choice for dirty water. The University of Florida fact sheet recommends it when water carries large amounts of algae or other organic contaminants, and the B.C. manual says to consider it whenever organic matter exceeds 10 mg/L. Its drawbacks: the largest footprint, the largest backflush volumes and a higher pressure loss.
Hydrocyclone (sand separator)
This is not a true filter. Water spins inside a cone and centrifugal force throws sand downwards. Agriculture Victoria says it removes sand of 50 microns and larger, typically from groundwater. The B.C. manual adds that it operates at a pressure drop of 5 to 11 psi, roughly 0.35 to 0.75 bar: below that, flow is too low to separate the particles. It goes upstream of a screen or disc filter, never on its own.
Choosing by water source
The right filter depends first on what the water carries. The table below summarises the recommendations of the sources cited, applied to the situations found on farms in West and Central Africa.
| Water source | Main contaminant | Recommended filtration |
|---|---|---|
| Borehole, clear water with no organic matter | Fine mineral particles | Screen or disc filter |
| Borehole that pumps sand | Sand of 50 microns and larger | Hydrocyclone, then screen or disc filter |
| River, stream, canal | Silt, debris, organic matter that varies with the season | Media filter with automatic backflush, then a screen or disc safety filter |
| Pond, dam, reservoir | Algae and organic matter | Media filter, coarse prefilter if there is debris, then a safety filter |
| Open storage tank fed by pumping | Algae growing in the tank | Cover the tank, then a disc or media filter depending on the load |
Two more points from the same manuals. Surface water changes quality through the year, so the University of Florida fact sheet advises automatic backflushing for it. And when reservoir water is very loaded, above 200 mg/L of suspended solids according to the B.C. manual, the reservoir can be designed as a settling basin to take load off the filter. The same manual notes that a reservoir can also increase the organic load through algae and bacteria growth.
Before ordering, have a water sample analysed, taken under real pumping conditions, ideally during the rainy season for a river, when the water carries the most.
Sizing the filtration grade
The basic rule is simple: the dripper manufacturer’s recommendation comes first. Without one, the references converge:
- Agriculture Victoria: 120 mesh or finer for drip, about 130 microns, and filtration of roughly 1/6 to 1/10 of the emitter outlet;
- University of Florida, AE57: without manufacturer guidance, filter to the equivalent of 74 microns, which is a 200 mesh screen;
- B.C. manual: for drip, remove particles larger than one tenth of the orifice diameter, with an absolute minimum of 80 mesh on any trickle system.
A finer filter protects better, but clogs faster and must be cleaned more often. The right setting protects the dripper without turning cleaning into a daily chore. Filter capacity must also match the peak flow of the largest section: an undersized filter creates a pressure loss that starves the drippers at the end of the line.
Knowing when to clean: read the gauges
A filter fouls gradually, and the only reliable way to know is to measure the pressure difference between inlet and outlet. Fit a pressure gauge on each side of the filter. Agriculture Victoria gives these benchmarks.
| Filter type | Clean head loss | Backflush before | Backflush water (share of water pumped) |
|---|---|---|---|
| Screen | 5 to 20 kPa (0.05 to 0.2 bar) | 50 kPa (0.5 bar) | 0.5 to 1 percent |
| Disc | 20 to 50 kPa (0.2 to 0.5 bar) | 70 kPa (0.7 bar) | 0.5 to 1.5 percent |
| Media | 30 to 70 kPa (0.3 to 0.7 bar) | 100 kPa (1 bar) | 2 to 5 percent |
Source: Agriculture Victoria, Filtration for drip irrigation.
On an automatic system, Agriculture Victoria advises triggering backflush on pressure differential, with a timer as backup. Watching that differential also reveals a torn screen or a tunnelled sand bed: a pressure difference that never rises is not necessarily good news.
Set-ups that really protect the network
- A safety filter after the media filter. The B.C. manual calls for a screen downstream of a media filter, to catch sand carried over during backflush or after a fault.
- At least two media tanks. One tank backflushes with clean water filtered by the other. Agriculture Victoria notes that backflushing a media filter needs a flow higher than the filtration flow.
- A coarse prefilter ahead of the media filter when the water carries leaves and debris.
- A filter after the fertiliser injection point, to catch precipitates formed at injection, as the same manual requires. The complete order of the control head for fertigation is set out in our article on fertigation through drip irrigation.
- Flushing line ends. Even with good filtration, open the end caps of the laterals regularly to clear deposits that build up where water moves slowest.
Checklist before ordering a filter
- Water source identified: borehole, river, pond or open tank.
- Water analysis done: suspended solids, organic matter, iron, hardness.
- Dripper manufacturer’s filtration recommendation known.
- Peak flow of the largest section calculated.
- Available pressure known, especially with solar pumping and an elevated tank.
- Two pressure gauges planned, before and after the filter.
- Backflush water discharge planned away from the plot.
- Person responsible for cleaning named, and frequency recorded in the irrigation logbook.
On a solar pumped site, filtration goes hand in hand with storage: a tank left open to light becomes a source of algae, and a filter placed at the tank outlet has to work at low pressure. We covered storage capacity in our article on sizing the water storage tank for a solar pumped pepper plot. For a complete installation example, see drip irrigation installation for ginger, and for the bigger picture, our guide to drip irrigation systems for African farms.
JOGOO filters and control heads
JOGOO Agriculture supplies and installs the control heads of its drip networks, including screen filters and disc filters, sized for your water source and flow. See the Irrigation & Pumping page for equipment, and the Turnkey Agricultural Projects page if you are equipping a new plot from start to finish. For a quote, tell us your water source, area and crop through the Contact page.
Frequently asked questions
Which filter for drip irrigation fed by a borehole?
If the water is clear with no organic matter, a screen or disc filter is enough; the University of Florida names the screen as first choice for well water. If the borehole pumps sand, add a hydrocyclone upstream.
Which filter for river or pond water?
A media filter, which holds back algae and organic matter, followed by a screen or disc safety filter. The B.C. manual advises a media filter whenever organic matter exceeds 10 mg/L.
What filtration grade does drip irrigation need?
Follow the dripper manufacturer first. Otherwise, Agriculture Victoria gives 120 mesh or finer, about 130 microns, and the University of Florida uses 200 mesh, which is 74 microns.
When should the filter be cleaned?
When the pressure difference between inlet and outlet rises. According to Agriculture Victoria, backflush a screen before 50 kPa of head loss, a disc filter before 70 kPa and a media filter before 100 kPa.
Disc filter or screen filter: which one?
A screen loses little pressure and takes little space, for average to good water. A disc filter holds more in depth and uses little backflush water, but has more parts and must be dismantled when clogged.
Is a hydrocyclone enough on its own?
No. It removes sand of 50 microns and larger, but it is not a true filter. It always goes upstream of a screen or disc filter.
Sources
- Agriculture Victoria, Filtration for drip irrigation
- Haman D. Z., Zazueta F. S., Media Filters for Trickle Irrigation in Florida, AE57, UF/IFAS Extension, revised 2024
- B.C. Trickle Irrigation Manual, Chapter 10, Filtration, 1999
