Black staining from water is typically composed of several different fungi.
Although unsightly, black stains caused by water don’t generally present a health risk – unless the fungal growth is allowed to continue unchecked and becomes very dense.
Then, any risk though would be from breathing in fungal spores (particular for those with illnesses such as asthma) – not from the water supply.
How to deal with black staining
The cold mains water supply contains a small amount of chlorine, which inhibits the growth of fungal spores.
However, water running through the internal plumbing system will gradually lose the protective effect of this residual amount of chlorine.
Once established, fungal growth can be difficult to get rid of.
- Improving ventilation and keeping surfaces dry is the best way to prevent growth.
- The most effective way of controlling re-growth is through regular cleaning with a bleach-based cleaning product, paying particular attention to areas where soap residue may accumulate.
- The cleaning process is generally more successful if the cleaning product is allowed to act for a while (about half an hour), before rinsing it off.
Using abrasive cleaning products tends to encourage re-growth as they cause a rough surface where the fungi can take hold.
This is why black growth is often seen on grout but not on tiles, unless they’re covered in heavy soap deposits.
We recommend that storage tanks which feed showers and internal plumbing are checked to make sure they aren’t open to the atmosphere. Installing a securely fitting lid should avoid dust and debris falling into the tank.
We also recommend that the tank itself is checked for sediment and deposits and cleaned if necessary. Deposits in the tank may reduce the amount of chlorine in the water and help create conditions in which fungi can grow.
We’d also advise disinfecting and drying bathrooms and kitchen surfaces before leaving the house vacant for long weekends or holidays. Pouring a little household bleach into toilet bowls and down the kitchen sink will help slow down any re-growth.
More about black staining
- Fungal spores are naturally present in the environment and being airborne, can be dispersed throughout buildings by air currents.
- When they find a suitable warm, moist location with a source of food, the spores multiply and produce a grey or black ‘jelly-like’ growth.
- In bathrooms, propellants from aerosols, hair spray, deodorants and soap residues provide a source of nutrients and can accelerate growth.
- Also when houses are left vacant over long weekends, holidays or in between occupancy, fungal spores multiply.
- The increased use of double-glazing and warmer buildings has contributed to fungal growth as there are less draughts, which help dry out the atmosphere.
- Water without chlorine present provides the moisture that these fungi need to grow, so they are usually found places such as:
- the end of cold water taps (usually kitchen or bathroom) such as the plastic inserts in kitchen taps
- inside washing machines, particularly around the powder drawer
- filter jug hoppers and their elements
- inside kettles, if water is left for long periods
- toilet cisterns and bowls, for example up under the rim and inside the cistern
- shower heads
- around tiles and sealants in bathrooms and shower rooms
- on shower curtains or towels (where they often appear as black spots or staining)
- in waste traps connected to sinks