# Filtration and Fertigation Procurement: A Checklist That Stops Rework Before It Starts
Filtration and fertigation sit where water quality, chemical dosing and hydraulic design meet, which makes them the easiest part of an irrigation project to under-specify — and the most expensive to correct after installation. A filter bank that is one size too small, an injector without the right turndown ratio, or a seal that cannot tolerate acid will all surface later as clogged emitters, uneven crop growth and emergency purchases. The checklist below is organised the way a procurement file should be built: system data first, component verification second, and commercial and documentation checks last.
Start With System Data, Not the Product Catalogue
Water quality baseline
Every filtration decision begins with a laboratory analysis of the actual water source, not a general description of it. The report should cover suspended solids and turbidity, sand and silt content, iron and manganese, hardness, pH, organic load and algae. Just as important is seasonal variability: a borehole that runs clear in winter may carry fines after heavy rain, and a reservoir that looks clean at the surface may draw algae and organic debris through the intake. Take samples from the point where the filter will actually be installed, and sample during the worst-case period you expect in the season.
Debris type then points to filter type. Inorganic sand and silt favour a centrifugal or media separator ahead of the fine stage; algae, organic matter and biofilm favour disc or screen filtration with a finer rating and more frequent flushing. In many projects the correct answer is a combination — coarse separation upstream, fine polishing downstream — and the procurement file should state that sequence explicitly so suppliers quote against the same duty.
Flow rate, pressure and peak demand
Filters, injectors and valves must be sized on peak simultaneous flow, not on average daily demand. Map the block layout, note how many zones can run at once, and build in a realistic allowance for future expansion. Then calculate the pressure budget: static inlet pressure, losses across the filter at the end of its cleaning cycle, losses across valves and fittings, and the minimum operating pressure required by pressure-compensating drippers or sprinklers at the furthest point. A filtration unit that performs on the test bench but consumes too much head in the field will quietly starve the emission devices downstream.
Chemical programme and network compatibility
Fertigation specifications only make sense once the chemical programme is known. List every product to be injected — soluble fertilizers, acids, chlorine or sanitising agents — with typical dilution ratios and injection durations. Confirm connection standards early: BSP or NPT threads, metric or imperial pipe diameters, flange drilling, and whether the assembly will be skid-mounted or field-built. For automatic systems, record the power supply, control voltage, signal types and the protocol expected by the central controller, so the fertigation unit arrives ready to integrate rather than ready to be adapted.
Filtration Checks — Verify Ratings, Materials and Maintenance Access
Match filter type and rating to the solids being removed
Screen, disc, centrifugal and media filters are not interchangeable, and the specification should state which duty each unit performs. Ask for the nominal micron or mesh rating, the rated flow per unit at a defined head loss, and the recommended number of units in parallel, including whether a duty/standby arrangement is needed for continuous operation. Note that published ratings are usually nominal rather than absolute, so a modest over-sizing margin is normal practice in agricultural systems. Where several filters are manifolded, confirm that inlet and outlet diameters keep velocity within sensible limits and that flow distribution across the bank is balanced.
Backwash, head loss and instrumentation
Cleaning method determines both water use and labour. Manual screen and disc filters are simple but demand attention; automatic backwash units need a reliable water source, correctly sized flush valves and a controller that can be programmed around the irrigation schedule. Specify pressure gauge ports upstream and downstream so differential pressure can be monitored, and ask whether differential pressure switches or transmitters are included. Check where backwash water will discharge, whether drainage falls by gravity, and how the system behaves in freezing conditions if the installation is above ground.
Materials, spares and serviceability
Housings, screens, discs, gaskets and fasteners should suit the water and the chemicals in use, with UV-stabilised plastics or coated metal where units sit in direct sun. Serviceability matters as much as durability: can the element be removed without tools, is there space around the unit for maintenance, and are replacement cartridges, discs and seals listed as separately orderable items?
Confirming these service details early with an irrigation equipment manufacturer usually reveals whether a design is genuinely field-maintainable or only looks that way in a brochure. A short spare parts list supplied with the quotation — filter elements, seals, gauges, solenoid valves — protects the project long after commissioning.
Fertigation Equipment and Commercial Checks That Protect the Project
Dosing accuracy and control method
Venturi injectors and proportioning pumps solve the same problem in different ways. Venturi units are simple and robust but depend on adequate pressure differential and stable flow; motor-driven proportioning pumps offer finer control and wider turndown but need power, maintenance and calibration. The specification should state the required injection rate range, whether dosing is flow-proportional or fixed, and how the unit interfaces with EC and pH controllers. Consider tank capacity, agitation for crystallising fertilizers, suction-line filtration to protect the injector, and the calibration method operators will use in the field.
Chemical compatibility and backflow protection
Fertilizer salts and acids attack the wrong elastomers quickly. Confirm diaphragm, seal and body materials against the actual chemical list, and require backflow prevention as a non-negotiable item: non-return valves, vacuum breakers, anti-siphon devices and clear separation between the water main and the stock solution. Secondary containment for tanks, ventilation for enclosed spaces and unambiguous labelling of injection points are inexpensive at procurement stage and difficult to retrofit later.
Documentation, spares and supplier capability
Close the file with commercial checks: datasheets, dimensional drawings, flow and head-loss curves, material specifications, packing lists and a spare parts schedule. Confirm warranty terms, lead times, consolidation of filtration and fertigation items into one shipment, and whether the supplier offers OEM or ODM work, customised assemblies or design support for larger projects. For distributors and public procurement buyers, request the exact model codes and quantities in writing so that delivery can be verified against the purchase order, and agree in advance how technical questions will be handled during installation and the first season of operation.
A Gothenburg marine-ecology graduate turned Edinburgh-based science communicator, Sofia thrives on translating dense research into bite-sized, emoji-friendly explainers. One week she’s live-tweeting COP climate talks; the next she’s reviewing VR fitness apps. She unwinds by composing synthwave tracks and rescuing houseplants on Facebook Marketplace.