Asked about the water supply

Why is our spring water brown after heavy rain?

Answered by Asked in Ayrshire · Updated 5 November 2026 · Sources at the foot

Spring water usually turns brown after heavy rain because the rain washes peaty organic matter from the hill into the source, and that colour can stop UV treatment working properly.

A burn in spate, brown and churning, rushing under an old stone bridge with a road and fields beyond. — A burn running brown in spate after heavy rain.

On Ayrshire's upland farms the pattern is familiar: a wet night, then a bath that looks like weak tea. The colour itself is not usually the danger. The trouble is what tends to arrive with it.

Rain that is strong enough to stain the water is also washing soil, animal droppings and anything else on the catchment into the source. That's why brown water after a storm deserves a call to the council rather than a shrug.

What makes the water brown?

Mostly peat. The Drinking Water Quality Regulator's guidance on colour says colour comes mainly from naturally occurring organic acids from peaty soils, with humic and fulvic acids common. It adds that after heavy rainfall a supply may well be highly coloured, so a sample that passed one week can fail the next.

The legal standard for colour is 20 mg/l Pt/Co. The compounds behind it are of no direct health significance, but they matter for treatment.

Is brown water a health risk?

It can be, indirectly. East Ayrshire Council warns that the risk of harmful bacteria rises after heavy rainfall or snowmelt and when the water is highly coloured.

Colour also weakens UV disinfection. The regulator's UV guidance says that if there is any visible colour at all, water is unlikely to be suitable for UV treatment, and turbidity needs to be below 1 NTU. So on a stormy day the lamp may be shining on water it can't properly treat; our UV page explains why pre-filters matter.

What should we do when it happens?

Follow any advice the council has given you, exactly as written. If you are unsure whether the water is safe, the cautious route is to use boiled or bottled water for drinking, ice, brushing teeth and preparing food until you've spoken to environmental health.

Note when it started, how long it lasted and what the weather did. That record helps the council decide what to sample and when, as explained on who tests a private supply. mygov.scot says to contact the council's environmental health department if the supply is disrupted and you can't identify the problem.

Can treatment cope with the colour?

Yes, with the right equipment in the right order. The regulator lists granular activated carbon and ion exchange "organic scavenger" resins as ways to remove the organic compounds, each needing correct sizing and regular replacement or regeneration.

mygov.scot advises that choosing treatment is best left to a specialist, and the private supply grant can help pay for it. Keeping animals away from the source and fitting well-sealed tank covers also helps reduce what gets washed in.

What to look at first

Is the colour only after rain, or all the time?
Is the UV lamp's alarm or indicator showing a fault?
Are the sediment filters visibly dirty or blocked?
Is the collection tank cover in place and the fence intact?
Has anything changed on the catchment, such as ploughing, forestry work or new livestock?

Yours to do, and theirs

You can

Use boiled or bottled water for drinking until you have spoken to the council.
Photograph the water and note dates and rainfall.
Change dirty filter cartridges as the maker describes, and keep spares.

Leave to them

The council's environmental health team samples the supply and advises.
An accredited lab tests for bacteria, colour and turbidity.
A water treatment specialist adds carbon or resin treatment ahead of the UV.

Brown water after rain: what it usually means
What you notice	Likely cause	Who to involve
Tea-coloured water for a day or two after rain	Peaty organic acids	Council, to sample at the right time
Cloudy or gritty water	Soil and sediment in the source	Check filters, then the council
Colour plus a UV fault light	Treatment not coping	Specialist, and the council
Colour all year round	Peaty catchment	Specialist to size carbon or resin treatment

Safety first

Coloured water can carry bacteria that UV is not killing. Until the council says otherwise, use boiled or bottled water for drinking and food, and follow any council notice exactly.

In short

Brown water after rain is usually peat washed into the source. The colour itself is not toxic, but it travels with run-off that can carry bacteria and it stops UV working well, so tell the council and drink boiled or bottled water until you know.

Also asked about this

Is iron the cause rather than peat?

It can be. Iron and manganese also reduce UV effectiveness, according to mygov.scot, and only a lab test will tell you which you have.

Why does the water clear after a day or two?

As the rain stops, less run-off reaches the source and the organic load falls. The regulator notes colour can vary widely with rainfall.

Does forestry work nearby matter?

The regulator's filter guidance warns that ploughing near the source can quickly clog filters, so tell the council about any big change on the catchment.

Will a jug filter make it safe?

No. A jug filter is not disinfection. Follow the council's advice on boiling or an alternative supply.