Since 6 September 2023, the mandatory content of a public works design in Portugal has been set by Ordinance 255/2023 — which replaced the 2008 one — and it has a section devoted to wastewater drainage and treatment. Phase by phase, it states what the designer must deliver, from the base design to the detailed design.
You would expect that to be enough. It is not, for a simple reason: the ordinance says what, and never says how much, measured how, or from what data. That is the tender specification — and it belongs to whoever is buying.
We read five sets of tender specifications for designs on existing treatment plants, contracted between 2021 and 2026, from €20,000 to €234,000, by five different entities — two of them in the same group, sharing the same boilerplate word for word. Two of the five specify no technical content at all: some twenty thousand characters each, and not one requirement on flow, phasing, pre-treatment, energy or effluent destination. They refer to the legislation. And legislation, on its own, returns the minimum.
There are five things you only get if you write them down.
1. The preliminary programme — which is yours, not the designer’s
The ordinance is clear: the preliminary programme is «o documento fornecido pelo dono da obra ao projetista» — the document supplied by the client to the designer. For a treatment plant it has its own elements (article 151): the design horizon, the current state of the area served, the existing infrastructure, the industries connected to the network and their discharges, and the receiving water body — «caudais de estiagem e características bioquímicas», low-flow rates and biochemical characteristics, included.
When the client does not supply them, the designer assumes them. And assumes what is reasonable, not what is true: the factory that discharges at night, the stream that runs dry in August. The preliminary programme is not paperwork; it is the only phase of the design written by someone who knows the plant.
The question to ask: who writes the preliminary programme — and from which operating records?
2. Measured flows, and who pays for the measuring
The base design calls for «capitações de consumo de água e coeficiente de afluência à rede» — per-capita water consumption and network inflow coefficient — and the «critérios adotados», the criteria adopted, for infiltration and stormwater (article 152). Criteria, not measurements. The law allows calculation.
Only the tender specification can require a flow measurement campaign in dry and wet weather before anything is sized, and state whether it sits in the design price or is the client’s own cost. Of the five specifications we read, two do not use the word flow once.
The question to ask: does the specification require measured flows, or accept flows calculated from population?
3. An energy balance with units, not with adjectives
Two of the five specifications require that «o cocontratante deverá optar, fundamentadamente, por soluções de engenharia que minimizem o consumo de energia potenciando a eficiência energética» — that the contractor shall opt, with justification, for engineering solutions that minimise energy consumption while enhancing energy efficiency. The intent is right — and it cannot be verified. “Minimise” has no number.
The ordinance goes further than those specifications: the detailed design must carry «consumos específicos» per unit process and the «balanço energético da instalação», the plant’s energy balance (article 155), along with operating costs across the design horizon — energy, reagents, sludge, maintenance. What is left is what the specification adds: the units (kWh per cubic metre treated and per kilogram of COD removed), the reference case (the plant as it stands today) and the flow scenarios the figure is computed under. With that, two bids can be compared. Without it, adjectives are compared.
The question to ask: does the specification state in what units, and against what reference, the energy balance is presented?
4. Phasing with the plant in service — and access to it
In a refurbishment with the plant running, the ordinance requires a «descrição detalhada do modo de construção especificando as várias fases de execução, bem como os principais impactes no modo de exploração» — a detailed description of the construction method specifying the execution phases and the main impacts on operation (article 155) — and, as early as the preliminary design, «testes, ensaios e inspeções», tests, trials and inspections of the existing structures and equipment (article 154).
No designer does this without entering the plant, reading the operating records and talking to the people who run it. The specification is where that access is secured — site visits, telemetry data, breakdown history — and where it is decided what gets tested before it is decided what gets replaced.
The question to ask: does the specification provide for access to the plant and its records, and state which tests on the existing works are included?
5. Who reviews the design
The ordinance defines design review as «análise crítica do projeto […] por outrem que não o projetista» — a critical analysis of the design by someone other than the designer. Among the 145 study and design contracts mentioning a treatment plant, awarded between 2021 and July 2026, nine are design reviews — and all of them from 2024, 2025 and 2026. It is few, and it is recent.
A review costs a fraction of the design and catches, before the works tender, what otherwise turns up as variations. It need not be a separate contract: it can be a clause in the specification — who reviews, at what phase, with what turnaround.
The question to ask: does the specification set out who reviews the design, and when?
The point
None of these five requirements is against the designer. A serious designer meets them anyway — and prefers a specification that writes them down, because that is what separates them from those who do not. What the specification does is stop the difference between the two from being settled on price.
The ordinance sets the minimum. The specification sets what you receive.
IdroAM Water Engineering designs and reviews wastewater treatment plant projects. If you are preparing tender specifications for a design, talk to us.
