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Sunday, 13. September 2026

How the water quality rating is calculated

The official sample and our calculation always stand side by side, never one on top of the other. The sample is legally binding and can be three weeks old. The calculation estimates whether anything speaks against today, and it is documented here in full so anyone can check it.

Load = distance to the source x weight of the source x current conditions, then the history factor of the zone.

Distance, straight line

unter 250 m1,00
unter 500 m0,75
unter 1 km0,45
unter 2 km0,20
unter 3 km0,08
darüber0

Weight of the source, all from official fields

nicht genehmigtx 1,30
in Bearbeitungx 1,15
Funcionamiento: No activo0
ohne oder unbekannte Behandlungx 1,35
nur Desbaste oder Tamizadox 1,20
Sekundärstufex 0,80
mit Desinfektionx 0,55
Leitungszustand Malox 1,20
häusliches Abwasserx 1,15
Salzsole oder Entsalzungx 0,45
habituelle Einleitungx 1,10

Conditions

f = 0.10 + 0.60 x rain + 0.30 x drift. Rain is the sum of the past 48 hours divided by 20 millimetres and capped at 1. Drift is the positive part of the cosine between the current direction and the bearing from the discharge to the beach, scaled with the speed. Several effective sources raise the result by 5 percent each.

Thresholds: from 0.55 red, from 0.22 yellow, below that green.

The history factor

Distance, permit status and weather do not know whether a discharge has ever reached this beach. The official samples do. The model calculation therefore passes through a factor taken from the zone own series, calculated as shares of the respective limit so that E. coli and enterococci are comparable. Damping only happens with evidence: below 20 samples the factor stays 1. A history of bans beats any damping.

Own series of the zoneFactor
5 oder mehr Badeverbote im Archiv1,40
mindestens ein Verbot oder eine Überschreitung1,20
unauffällig, p90 über 35 Prozent des Grenzwerts1,00
p90 unter 35 Prozent0,90
p90 unter 15 Prozent0,75
p90 unter 5 Prozent0,55
weniger als 20 Proben1,00

Limits

Legal limit in coastal water under RD 1341/2007, sufficient class: 500 cfu per 100 ml for E. coli, 185 cfu per 100 ml for intestinal enterococci.

This page does not replace official bathing water monitoring or a warning issued by the municipality. The estimated part is our own calculation, not a measurement.

Sources: Gobierno de Canarias (Dirección General de Salud Pública; Censo de vertidos desde tierra al mar), Ministerio de Sanidad (NÁYADE), European Environment Agency (UWWTD), Ministerio para la Transición Ecológica, Open-Meteo. Data as of: 2026-09-13, 22:18