Green water can have several different causes. In lakes, ponds and surface waters, algae and biological activity are the most common explanation. In buildings, pools and technical systems, green discoloration may instead be caused by metals, corrosion or chemical reactions. Correct diagnosis is therefore essential before selecting a treatment solution.
Green coloration does not necessarily indicate unsafe water, but a sudden change in colour or clarity should always be investigated. Chemically, green and blue-green shades are often caused by dissolved metal ions or corrosion products. Copper is the most common cause and may produce colours ranging from pale blue to turquoise or green depending on concentration, pH and other water chemistry conditions. Nickel, chromium and certain other metals may also contribute to green colours under specific circumstances. In lakes and reservoirs, however, microscopic algae and cyanobacteria containing natural pigments are often responsible.
Did You Know?
Green water in lakes and ponds is often caused by microscopic algae suspended in the water. Under favourable conditions these organisms can reproduce rapidly and create a noticeable green colour. In drinking water systems, however, green shades may instead originate from copper compounds or corrosion products released from plumbing installations.
The colour of water can often provide clues about the underlying chemistry. Copper ions frequently produce blue or turquoise shades, nickel may under certain conditions create green tones, while iron typically causes yellow, orange or brown colours. For this reason, water chemists can sometimes obtain an initial indication of the cause simply by observing the colour, although laboratory analysis is always required for confirmation.
Common Causes
- Algae and Biological Growth
- Cyanobacteria (Blue-Green Algae)
- Copper from Plumbing or Equipment
- Corrosion of Plumbing Systems
- Insufficient Disinfection in Pools or Spas
- Biological Growth in Tanks or Reservoirs
Common Symptoms
- Green or Greenish Water Colour
- Reduced Clarity
- Deposits on Surfaces or in Tanks
- Increased Biological Activity
- In Some Cases Odour or Taste Issues
Common Treatment Methods
- Water Analysis
- Filtration
- UV Disinfection
- Ozone
- Activated Carbon
- Inspection of Corrosion and Metal Levels
Example Treatment Trains
Raw Water
↓
Filtration
↓
Ozone
↓
Activated Carbon
↓
UV Disinfection
↓
Drinking Water
Water Analysis
↓
pH and Corrosion Assessment
↓
Corrective Actions
↓
Normal Operation
Green water may have biological, chemical or technical causes. Since the same colour change can originate from very different mechanisms, the root cause should be identified before selecting a treatment solution. Water analysis is often the fastest way to determine whether the issue is related to algae, metals, corrosion or other factors.