Two percentages in a water report can answer different questions. One may describe whether the planned tests were completed; another may describe whether their results met the relevant limits. EPAL's Lisbon consumer-tap report provides a useful example of why both the headings and the follow-up explanation matter.
Before reading the figures, choose the series that matches the water you are asking about.
Find the consumer-tap series
EPAL's data-publication guide separates consumer taps in Lisbon from fixed distribution-network points, delivery points to other operators, the transport system and source-water monitoring. For a household-supply question, begin with consumer taps. A raw-source result describes a different sampling point.
EPAL describes Lisbon's distribution network as one supply zone and says compliance samples are taken at consumers' drinking-water taps. When read on 14 October 2026, the consumer-tap index contained monthly 2026 files and a second-quarter 2026 summary. Read the collection period inside the file; downloading it later does not change the period covered.
Follow the two percentages through one example
The second-quarter 2026 report, dated 11 August 2026, separates sampling-plan completion from parametric compliance, the share of results meeting the applicable limits.
For the total-coliform bacteria test, 373 analyses were planned and 373 completed, giving 100% completion. The same row records 16 above-limit results and 95.71% parametric compliance. The test row labelled enterococci/fecal streptococci records four results above the limit. These are the report's named bacterial test rows. Completing the programme and meeting the limits therefore need to be read separately.
EPAL says repeat analyses showed a return to normal and confirmed no problem significant for public health. It suggests possible contamination at the sampled consumer taps. That is the utility's follow-up explanation, not an independent diagnosis of a particular building. Keep the exceptions and that explanation together when summarising the report.
For a trend comparison, record each file's supply area, sampling point, collection period, parameter and unit. Differences between those details can make two figures unsuitable for a direct comparison.
Put source and building information alongside the report
EPAL's water-origins page lists surface-water intakes at Castelo do Bode on the Zêzere and Valada on the Tagus, plus groundwater sources in Lezírias, Ota and Alenquer. It describes the supply system without assigning a current source percentage to an accommodation's tap.
The utility's FAQ says the age and condition of building pipes and pressure equipment can affect taste, smell and colour. It recommends replacing lead pipes to minimise lead in water. This is general advice, rather than an inspection of a particular property.
Ask the host which supply serves the accommodation, whether a current notice applies and who handles the plumbing. Our Lisbon tap-water guide covers the broader traveller question; EPAL's dated reports answer the sampling questions described here.
