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What actually comes out into the bucket? My neighbour showed me a photo of black water and I can't believe it

Editorial guide · Updated 18 September 2026

In short Short answer: yes, and at 4 years it is normal – the black water is biofilm (bacteria + fungi + their sticky matrix), fine dust that passed the filters and stuck to the wet fins, and the sludge from the pan. The face of the unit is just plastic; the dirt is on the evaporator behind the filters and above all on the fan roller, which you cannot see without a torch.

This page explains a situation in an editorial format. It is not an open discussion board or a verified customer review. Contact us on WhatsApp about your own appliance.

Situation discussed

My neighbour across the landing (Rahova, 1980s block) had her unit cleaned and showed me a bucket of coffee-coloured water. My unit (12,000 BTU LG, 4 years old, living room) looks clean from the front, filters are fine. Can something like that really come out of a unit that looks good? What is actually in that water?

Editorial explanation · Revizie AC

What is really happening

Measurements on household units found the highest bacterial load in the condensate pan, dense Methylobacterium-dominated biofilm on the evaporator – a bacterium that resists drying and thermal shock – and the fan roller as the most fungus-contaminated component. All of that is wet, brown-black and smells – exactly what you see in the bucket. The alkaline detergent lifts the matrix off the aluminium and the jet carries it into the cover; the water colour goes from black to grey to clear as the surfaces come clean, which is why the white bucket is our control instrument, not just a container.

Explanatory diagramA cleaning cover directs wash water to a container
A cleaning cover directs wash water to a container
  1. The area and sensitive components are protected before work.
  2. The cover collects wash water.
  3. The hose directs water into a container.
What the studies say

What we do on site

  1. We show you the roller through the bottom grille with a torch before fitting anything – the moment your neighbour turns out to be right.
  2. Foil on the floor and furniture; double cover sealed to the wall; 2 m hose into the white bucket.
  3. Alkaline detergent on the evaporator, roller and pan; 5–10 minutes.
  4. Adjustable pressure wash in place; the first bucket is black, the second grey, the third clear – we photograph each.
  5. Pan and hose flushed until clear outside; sanitising; filters; outdoor unit washed in place.
  6. Drying on 'Fan', test; the bucket and after-roller photos on WhatsApp. See current rates on the Prices page.

What you can do yourself

  • Take a torch and look through the bottom grille right now, with the unit off – you will see the roller.
  • Filters every two weeks and 'Fan' for 20 minutes – they slow it, they do not stop it.

What NOT to do

  • Do not judge the unit by its front.
  • Do not pour bleach into the bucket 'to disinfect' – it goes to the drain, not into the unit.

Prevention

At 4 years, the first clean; then yearly – the bucket water gets less black year on year.

When to call us

0764 012 943, WhatsApp, Monday–Saturday 08:00–20:00; Rahova is 15 minutes away.

Cover fitted on the unit, hose running neatly into the white bucket, spotless living room
Cover fitted on the unit, hose running neatly into the white bucket, spotless living room
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Sources (4)

The information on this page is educational and based on cited sources; it does not replace medical advice. We do not do repairs, installation or refrigerant circuit work.