Irrigation Filters

Why filtration is the first design decision

Drip emitters release water through orifices around 0.8–1.4mm. Particles smaller than that enter the emitter and stay — one clogged orifice per row, and uniformity is gone; enough of them, and the line is dead. Every other component in the system can be under-specified and repaired; a system without the right filtration fails predictably, within a season, in the part that's most expensive to replace. That's why the water source assessment comes first in the design: the filter follows the water.

See the full logic in the filtration guide and the water quality guide — this page is the equipment side.

The three filter families

Matching filter to water source

• Borehole: usually the cleanest source, but not always — some boreholes carry iron (which oxidises and clogs slowly) or fine sand. A disc filter is the standard fit; where iron is present, the design adds an oxidation/flushing provision or a finer routine. Confirm with a look at what the water does after sitting in a clear jar for a day.
• Storage tank: a disc filter handles most tank water. Where the tank is open and algae grow, keep the first stage coarse (a screen) before the disc, and clean the tank.
• Dam: season decides. A clean dam in the dry season may run a disc; the same dam in the rains wants a sand stage in front of it. If the dam is your only source, specify for the worst week, not the average one.
• River: a sand/media filter is the working standard, with a disc or screen second stage for fine polishing — and an intake strainer before the pump. River filtration is where "cheap kit" systems die first.
• Rainwater harvesting: first-flush provision on the roof catchment plus a disc filter is usually enough; roof debris (bird, leaf) is the main load.

Two-stage setups (sand + disc) are common on surface water, and a screen stage is added anywhere the emitters are very fine (seedling lines, point-source drippers).

Sizing

The filter is sized to the system's design flow — the pump's flow, practically. A filter run at twice its rated flow doesn't filter; it just leaks slowly. At smallholder scale one disc unit is typical; commercial systems carry multiple units in parallel so one can be cleaned while the others run. The sizing is in the design, not on the box.

Maintenance — the part that decides the outcome

• Watch the pressure drop. Every filter has an inlet/outlet gauge pair; a rising differential is the filter telling you it's dirty. Backwash or clean at the specified drop (commonly 0.5 bar), not when the field complains.
• Disc filters: disassemble, rinse the stack under clean water, reassemble. Weekly in season for surface water; less often for clean borehole water.
• Sand filters: backwash per the unit's cycle (often 10–30 minutes of reversed flow); the waste line goes somewhere it shouldn't — plan the discharge.
• Screens: rinse, inspect the mesh for tears, replace when worn.
• Never run the system bypassing the filter "just this once" — the one bypass is the one that kills a season of emitters.

These routines are short and calendar-friendly; they're written into every design we deliver, and the maintenance guide lays them out as a schedule.

Fertigation and filtration

If you fertilise through the line, the stakes on filtration rise: a dirty filter plus a fertigation tank is how whole systems get clogged with precipitate. The injection point sits after the filter, and the flush routine after each feeding keeps the fertigation plumbing clear.