Comparing irrigation quotes in Nigeria: what to check.

Why totals mislead

Two quotations can cover different areas, different equipment and different work. One may include installation, testing at handover and training; another may leave them out, or leave them vague. Compare the lines first and the totals last.

FAO's handbook on pressurised irrigation says that once a design is complete, a list of all the equipment needed, called a bill of quantities, must be prepared with full descriptions, standards and specifications for every item, and that smaller purchases can be made on written quotations from two or three suppliers. If you can, send every supplier the same site details and ask each to quote line by line.

Source: FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 5: Equipment, standards and tenders for supply.

What a complete quotation states

Every design rests on a few figures. Flow is how much water passes in a set time: litres per hour (L/h) for a dripper, or cubic metres per hour (m³/h) for a pump or a pipe. One cubic metre is 1,000 litres. Pressure is how hard the water pushes inside the pipe, measured in bar. Head is pressure given as a height of water, in metres: one bar is about 10 metres of head. A pump's total head is the height it must lift the water, plus the pressure the system needs at the far end, plus what is lost to friction in the pipes, fittings, valves and filters, all in metres.

A complete quotation states:

• ☐ The design basis: the area, the crop or planting, the water source, and the flow and pressure the design needs
• ☐ A drawing of the layout: where the pump, mains, valves and zones go
• ☐ Makes and models of the main parts: pump, filter, controller, valves, and drip lines or sprinklers
• ☐ Quantities, sizes and materials for every item, and the pressure rating of the pipes
• ☐ For the pump: its power, whether an engine or a motor drives it, and the flow it gives at the total head the design needs
• ☐ What installation includes, such as trenching, connections and backfilling, and what you must provide
• ☐ The tests at handover, and who attends them
• ☐ Training for the person who will run the system, and a written user manual
• ☐ Drawings of the system as installed, and a maintenance plan
• ☐ Warranty terms for the equipment and for the workmanship, in writing
• ☐ Delivery time, payment stages, how long the prices hold, and what is excluded

Sources: FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 2: system pressure and flow capacity; FAO (2007), Handbook on Pressurized Irrigation Techniques, annex: units conversion table; FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 5: Equipment, standards and tenders for supply; USDA-NRCS (2020), Conservation Practice Standard 441: Irrigation System, Microirrigation, plans and specifications, operation and maintenance; FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 19: Engineering investigation.

Lay the quotes side by side

Put the quotations next to each other and tick each line where it is stated clearly. A gap or a vague line is a question to ask the supplier, not a reason on its own to turn a quotation down.

A comparison table

Use the table as a checklist for each quotation. The last column shows what should prompt more questions.

Sources: FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 5: Equipment, standards and tenders for supply; FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 20: Operation and maintenance; USDA-NRCS (2020), Conservation Practice Standard 441: Irrigation System, Microirrigation, plans and specifications, operation and maintenance.

Tests to ask for at handover

Commissioning is the testing at handover that shows the system works as designed. FAO's handbook notes that a system sometimes falls short because of poor design, faulty installation or equipment that does not meet its specification. As checks during the season, it lists pressure readings at the start and far end of the mains and submains, and at the first and last emitters, all within the designed range; the same readings make a good handover test.

For drip, UF/IFAS Extension recommends measuring emitter output at a minimum of 18 points in each zone: near the inlet, the middle and the far end, and at high and low spots. On a new system this shows whether it was properly designed and installed, and gives a reference for later checks. Ask for:

• Pressure readings at the pump, at the start of each zone and at its far end, written down
• The flow at the pump, read from a meter or timed with a container
• Emitter output caught in cups for a set time, near the start, middle and far end of each zone
• Filters cleaned, and every line flushed before planting
• The controller set, and shown to whoever will run it
• A copy of every reading, kept for later checks

Irrigation maintenance through the season↗

Sources: FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 20: Operation and maintenance; UF/IFAS Extension (n.d.), Field Evaluation of Microirrigation Water Application Uniformity, BUL265/AE094: evaluation procedure; USDA-NRCS (2020), Conservation Practice Standard 441: Irrigation System, Microirrigation, plans and specifications, operation and maintenance.

Questions to ask about the warranty

Warranty terms differ from one supplier and one maker to another. Ask for them in writing, as part of the quotation or the contract, and ask:

• Which parts are covered, and for how long?
• Is the workmanship covered as well as the equipment?
• Who pays for labour and transport when a part is replaced?
• What would cancel the warranty, such as missed maintenance or unfiltered water?
• Who do you call, and how soon will someone come?

Source: FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 5: Equipment, standards and tenders for supply.

Spares and support

A system is only as good as the repairs you can get in the dry season. FAO's 2016 country profile reports that only 63 percent of Nigeria's boreholes, most of them for public water supply, were working; the pumps of the others had broken down.

Ask which spares come with the system, such as filter elements, emitters, fittings and a pressure gauge; where further parts come from; who can repair the pump; and how long a part that is not in stock takes to arrive.

Source: FAO (2016), AQUASTAT Country Profile: Nigeria, water use section.

Running costs to count

A quotation shows what a system costs to buy; ask what it will cost to run. NRCS advises that a comparison of designs should count the operating costs as well as the equipment and its installation. Ask each supplier for the figures behind these lines, and count them over the seasons you expect the system to work:

• Power or fuel: what the pump draws or burns, from its data sheet, times the hours it will run in the hottest weeks
• Filter cleaning and line flushing: how often, and how long each takes
• Parts that wear, such as emitters, drip lines, seals and filter elements
• Labour to run and check the system
• The water itself, if you pay for it or buy it by tanker

Benefits and costs to count↗

Sources: USDA-NRCS (2020), Conservation Practice Standard 441: Irrigation System, Microirrigation, considerations; FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 20: Operation and maintenance.

Warning signs

• No questions about your water source, your area or your crop
• A total with no list of items
• Makes, models or sizes left out
• No test at handover, no training and no manual
• A warranty promised but not written down
• A total far below the others, with no reason given
• A demand to pay in full before anything is delivered