A pale yellow or tea-coloured tint in rainwater is often associated with tannins — natural organic compounds washed from leaves and other plant material on the roof catchment. Disturbed sediment, corrosion and other contaminants can also affect colour, so persistent or sudden changes should be investigated rather than diagnosed from colour alone.
What are tannins?
Tannins occur naturally in vegetation. Leaf litter and organic matter can release coloured compounds that are carried from the roof into the tank. The water may look clear in a glass yet create an obvious yellow tint in a white bath or basin.
Welcome to one of the realities of living on tank water: the catchment is part of the water system. What lands on the roof can influence what arrives in the tank.
Why ordinary filters may not fix it
Sediment cartridges are designed primarily for suspended particles. Carbon can improve some tastes and odours, but standard cartridge arrangements do not reliably remove every dissolved colour compound. Replacing filters repeatedly without identifying the cause can become expensive while the colour remains.
Specialist treatment for persistent dissolved colour may be possible, but it should follow assessment of the source, water chemistry, flow requirements and ongoing maintenance cost.
What should be checked first?
A tank clean is often the first practical recommendation where organic loading and sediment have accumulated. It removes material already sitting in the tank, although it cannot prevent new tannins entering from an unmanaged catchment and cannot guarantee removal of dissolved colour already present.
- Inspect the roof, valleys and gutters for leaf load and decomposing organic matter.
- Check first-flush devices, inlet screens and overflows.
- Assess the tank for accumulated bottom sediment.
- Note whether the colour occurs at every tap, only hot water, or a single outlet.
- Consider testing if the change is unexplained, persistent or accompanied by other concerns.
Frequently asked questions
- Are tannins harmful?
- Colour believed to be tannin should not be used by itself to make a safety conclusion. If water is intended for drinking and its quality is uncertain, appropriate testing and professional advice are preferable.
- Will UV remove yellow colour?
- No. UV systems disinfect water under suitable operating conditions; they do not physically remove tannins, sediment or dissolved colour.
- Why is the colour easiest to see in the bath?
- A bath provides a deep volume against a light background, making subtle colour more visible than it is in a drinking glass.