Water Quality Fault Finder: Discoloured, Smelly, or Unusual-Tasting Water

Summary

Water quality problems in UK homes fall into two broad categories: problems caused by the mains supply (where the water company is responsible) and problems caused by the building's own plumbing installation. Distinguishing between the two is the first diagnostic step — if neighbours on the same supply are experiencing the same issue, the problem is likely with the mains supply; if the problem is isolated to one property or one outlet, it is likely an internal problem.

UK tap water is regulated under the Water Supply (Water Quality) Regulations 2016 (England) [verify equivalent for Scotland, Wales, Northern Ireland] and must meet strict quality parameters set by the Drinking Water Inspectorate (DWI). Water companies are legally required to supply water that is wholesome — free from any organisms or substances that would harm health, and free from tastes or odours that would cause it to be rejected. If tap water fails to meet these standards, the water company must investigate and remedy the failure.

Internal plumbing problems — stagnant dead legs, corroding pipework, incorrectly sized cylinders, contaminated storage tanks — are the responsibility of the property owner and are typically addressed by a plumber. WRAS (Water Regulations Advisory Scheme) guidance is the key technical reference for plumbing installation that maintains water quality.

Key Facts

• Water Supply (Water Quality) Regulations 2016 (England; equivalents in devolved nations) — Define "wholesome" water and set parametric values for metals, microorganisms, and other substances
• DWI (Drinking Water Inspectorate) — Regulates water companies in England and Wales; accepts reports of poor water quality and can require water companies to investigate
• Water company notification — If mains water quality is poor, call the water company's customer helpline; they have a legal obligation to investigate; in Scotland, Scottish Water; in Northern Ireland, NI Water
• WRAS (Water Regulations Advisory Scheme) — Technical guidance on compliant plumbing installations; water fittings approval for materials in contact with drinking water
• Sulphur-reducing bacteria (SRB) — Anaerobic bacteria that metabolise sulphate and produce hydrogen sulphide gas; thrive in warm stagnant water; typical in dead legs, oversized cylinders, or cylinders not reaching pasteurisation temperature
• Legionella risk — Legionella pneumophila thrives between 20°C and 45°C in stagnant water; hot water cylinders should be maintained at 60°C minimum (60°C kills Legionella within 2 minutes); cold water should be below 20°C at outlets
• Lead plumbing — Houses built before approximately 1970 may have lead supply pipes (between the water main and the stopcock) or lead branch pipes; lead dissolves into soft, acidic water; contact the water company for supply pipe replacement in England (often subsidised)
• Blue/green staining — Copper dissolution in soft, acidic water; common in properties served by soft water (much of Scotland, Wales, and parts of the South West); not acutely toxic but indicates corrosion
• Black particles — Typically from degraded rubber components (washers, flexible hoses, diaphragms, flexible supply hoses behind taps); common after new rubber fittings have been installed or old rubber has begun to degrade
• White particles / flakes — Limescale from heating elements or scale build-up in scale-prone systems; detached from cylinder or heating elements; harmless but indicates hard water or overheating

Decision Tree

WATER LOOKS UNUSUAL OR TASTES/SMELLS ODD
│
├── Is the problem at ALL outlets in the property?
│   ├── YES → Check if neighbours are affected
│   │   ├── YES → Mains supply problem — call water company
│   │   └── NO → Internal problem, likely at or after the incoming stopcock
│   └── NO → Problem is localised → see below
│
├── COLOUR PROBLEM
│   ├── Brown / orange / rust-coloured
│   │   ├── Comes and goes, worse after no use → Iron from internal iron pipes or tank
│   │   ├── Sudden onset, clears after running → Disturbed mains (roadworks, burst pipe nearby)
│   │   └── Persistent, hot water only → Corroding cylinder thermostat or anode; or iron from header tank
│   │
│   ├── Blue / green staining on fittings and surfaces
│   │   └── Copper dissolution — soft/acidic water attacking copper pipes
│   │       → pH test of cold supply; check if property is in soft water area
│   │       → Consider phosphate dosing unit or water conditioner
│   │
│   ├── Black particles in water
│   │   └── Degraded rubber washers, diaphragms, or flexible hoses
│   │       → Check age of flexible hoses (replace every 5–10 years)
│   │       → Check ball valve diaphragm in cistern/header tank
│   │
│   └── White particles / cloudy white
│       ├── Cloudy, clears from bottom up when glass left to stand → Air bubbles (harmless, often after pressure change)
│       └── Particles that sink → Limescale from hot water system
│           → Check cylinder temperature; descale appliances
│
├── TASTE OR SMELL PROBLEM
│   ├── Rotten egg / sulphurous smell
│   │   ├── Hot water only → Sulphur-reducing bacteria in cylinder or dead leg
│   │   │   → Check cylinder temperature (should reach 60°C); eliminate dead legs
│   │   │   → Increase cylinder thermostat; consider chlorination
│   │   └── Cold AND hot water → Possible mains supply or storage tank contamination
│   │       → Call water company; inspect open header/storage tank for contamination
│   │
│   ├── Chlorine / bleach taste
│   │   └── Water company temporarily increasing chlorine (common after mains work)
│   │       → Run cold tap for 2–3 minutes; use filter jug if persistent
│   │       → Notify water company if persistent (above normal levels)
│   │
│   ├── Metallic taste
│   │   ├── New copper pipework → Will diminish as passivation layer forms; flush system
│   │   └── Lead taste (rare but important) → Lead supply pipe or internal lead pipes
│   │       → Contact water company for free supply pipe test; check age of property
│   │
│   └── Earthy / musty taste
│       └── Algae or organic contamination in open storage tank or header tank
│           → Inspect tank for light ingress, contamination, lack of cover
│           → Clean, disinfect, and re-cover tank
│
└── SUSPECT HEALTH RISK
    └── Any water that may be contaminated with sewage, chemicals, or biological matter
        → Do not use the water for drinking or cooking
        → Call water company immediately
        → If serious contamination risk, contact local authority Environmental Health

Detailed Guidance

Brown/Orange Water — Iron and Manganese

Iron in tap water is one of the most common water quality complaints in the UK. It presents as brown, orange, or rusty discolouration, typically more noticeable in the first draw of water after a period of non-use (e.g., first use in the morning).

Sources:

• Internal iron pipework: Properties built before approximately 1960 often have iron or galvanised iron supply pipes and rising mains. These corrode internally, releasing iron particulates and dissolved iron into the water. The solution is replacement of the iron pipework with copper or plastic.
• Disturbed mains supply: Nearby mains work (pressure surges, burst pipes, valve operation) can disturb sediment in the water mains, causing a temporary discolouration that clears within hours. If this is the cause, the water company will be aware.
• Iron header tank or storage tank: Old galvanised tanks in cold roof spaces corrode and release iron. Replace with a plastic cistern.
• Corroding cylinder: An immersion heater or anode in a hot water cylinder can corrode if the cylinder is old or if the pH of the water is low. This typically affects hot water only.

Rotten Egg Smell — Sulphur-Reducing Bacteria

A hydrogen sulphide smell (rotten eggs) in hot water is a reliable indicator of sulphur-reducing bacteria (SRB) in the plumbing system. SRB are anaerobic bacteria that convert sulphate in the water to hydrogen sulphide gas. They thrive in warm, stagnant water — precisely the conditions found in an undersized cylinder, a dead leg, or a cylinder that never reaches pasteurisation temperature.

Diagnosis: If the smell is present in hot water but not in cold water drawn from the same mains supply, the source is internal to the hot water system. Check:

• Cylinder temperature: The thermostat should maintain the cylinder at 60°C minimum. At 60°C, Legionella and most other waterborne bacteria are killed within 2 minutes. If the thermostat is set too low (below 55°C), bacteria can proliferate.
• Dead legs: Any section of pipework that is not regularly flushed (disused outlets, capped-off branches, infrequently used taps) provides a stagnant habitat. Identify and remove or regularly flush all dead legs.
• Cylinder size: An oversized cylinder (relative to usage) means the lower portion of the cylinder rarely reaches pasteurisation temperature. Consider reducing the cylinder capacity or increasing usage patterns.

Treatment: Raise the cylinder thermostat to 60°C. Run all hot taps until the temperature at the outlet reaches 50°C+. For persistent SRB, the system may need chemical disinfection (chlorination). Contact a plumber or a water hygiene specialist.

Legionella note: SRB colonisation in a cylinder is also a risk marker for Legionella. In domestic properties with a single household, the Legionella risk is lower than in commercial buildings, but the same principles of temperature control and dead leg elimination apply.

Blue/Green Staining — Copper Dissolution

Blue or green staining on baths, basins, shower trays, and around taps indicates copper is dissolving from the pipework into the water. This occurs when the water is soft and slightly acidic — conditions common in Scotland, Wales, the Lake District, and parts of the South West, where the water originates from upland catchments with little dissolved calcium to buffer the pH.

Diagnosis: Check whether the property is in a soft water area (contact the water company or check the water company's website for water hardness data). Test the pH of the cold supply: a pH below 7.0 indicates acidic water that will attack copper pipework.

Resolution:

• Phosphate dosing units: A small inline dosing unit adds a food-grade phosphate to the water, which forms a protective film on copper surfaces and reduces dissolution. This is the standard approach for properties in soft water areas.
• pH correction filters: A calcite filter upstream of the property raises the pH of the water, reducing its aggressiveness to copper.
• Plastic pipework: Plastic (MDPE, PEX, or CPVC) is immune to the corrosion that affects copper. New installations in soft water areas are often specified in plastic for this reason.

Copper at low levels (below 2 mg/l) is not harmful to health. At higher levels (above approximately 3 mg/l in the short term), copper can cause gastrointestinal symptoms. The WHO guideline value is 2 mg/l.

Chlorine Taste and Odour

A noticeable chlorine taste or smell in tap water is not unusual in the UK and is generally harmless. Water companies add chlorine (or chloramine) as a disinfectant to ensure the water remains microbiologically safe throughout the distribution system. The level is controlled to the lowest effective level but can vary with demand, temperature, and following mains maintenance.

If the chlorine taste is sudden, very strong, or accompanied by other symptoms, contact the water company. Otherwise, running the cold tap for 1–2 minutes will significantly reduce the chlorine level. A filter jug (activated carbon filter) removes chlorine and chlorine taste effectively.

Metallic Taste — New Copper

New copper pipework releases a small quantity of dissolved copper into the water until a stable oxide passivation layer forms on the pipe interior. This typically takes 3–6 weeks of regular use. The taste is metallic and slightly bitter. Run the cold tap for 30–60 seconds before using water from recently installed copper pipework, particularly first thing in the morning.

Reporting to the Water Company

In England and Wales, customers experiencing poor water quality should contact their water company. The water company has a legal obligation under the Water Industry Act 1991 to supply wholesome water and to investigate complaints. For persistent problems or where there may be a risk to health, the DWI can also be contacted directly.

In Scotland, contact Scottish Water. In Northern Ireland, contact NI Water.

Frequently Asked Questions

Is brown water from the tap dangerous to drink?

Not usually, in terms of acute health risk — iron and manganese cause aesthetic problems (colour, taste) rather than immediate health effects at the levels typically found in tap water. However, if the discolouration is caused by bacterial contamination, sewage ingress, or an unknown source, do not drink it. If in doubt, do not use the water for drinking or cooking until the cause is confirmed.

The hot water smells fine but the bathroom smells like rotten eggs. What is this?

A sulphurous smell localised to a bathroom drain rather than from the tap indicates blocked or partially blocked drain with organic decomposition, or a dry trap allowing drain smells to enter the room. Run the shower and taps to refill the trap. If the smell persists, investigate the drain.

My water is cloudy but clears from the bottom of the glass up when left to stand. Is this a problem?

No. This is dissolved air coming out of solution as the water pressure drops and temperature rises at the tap. It is particularly common in cold weather when water is cold (holds more dissolved air). Completely harmless. If the water is cloudy and does NOT clear, or if the cloudiness is white and the particles settle, investigate further.

I have lead pipes. How urgent is this?

Lead from supply pipes dissolves into water and accumulates in the body over time. It is particularly harmful to children and pregnant women. If you have lead supply pipes (between the water main and your stopcock — these are typically dull grey and bend easily), contact your water company. Many water companies in England offer subsidised or free supply pipe replacement. As an interim measure, run the cold tap for 30–60 seconds each morning before using water for drinking or cooking (this flushes the water that has been in contact with the lead pipe overnight).

Regulations & Standards

• Water Supply (Water Quality) Regulations 2016 (SI 2016/614, England) — Sets parametric values for water quality and legal obligations of water companies

• Water Supply (Water Fittings) Regulations 1999 — Requirements for water fittings to prevent contamination of the supply

• Water Industry Act 1991 — Water companies' legal obligations to supply wholesome water and investigate complaints

• HSE L8 (Legionella: The control of legionella bacteria in water systems) — Approved code of practice for Legionella control; relevant to hot and cold water systems in domestic and commercial properties

• Drinking Water Inspectorate (DWI) — Regulatory body for water quality in England and Wales; accepts water quality complaints

• WRAS (Water Regulations Advisory Scheme) — Technical guidance on water fittings and plumbing installation standards

• HSE — Legionella and hot water systems — Guidance on Legionella risk in domestic and commercial buildings

• Scottish Water — Water quality information and complaints for Scotland

• NI Water — Water quality information and complaints for Northern Ireland

• no hot water — Hot water system fault finding

• low pressure — Diagnosing low water pressure at taps and showers