Borehole water usually looks clean from the tap, but groundwater is chemically complex and almost never ready to use untreated. Because the water sits in an oxygen-free aquifer, it carries dissolved metals, gases, hardness and sometimes pathogens that only reveal themselves — as stains, scale, smell, fouled membranes or failed samples — once it reaches the surface. This page explains every common borehole water problem: what it is, why it happens, and what it does to your plant.
Almost every borehole problem traces back to one fact: the water has no oxygen.
Deep groundwater is typically anoxic — it has been isolated from the air for years. In that reducing, often slightly acidic, environment, metals stay dissolved and invisible, carbon dioxide builds up, and sulphate can reduce to hydrogen sulphide. The water looks crystal clear at the wellhead. The moment it meets air — in your tank, pipe, membrane or sample bottle — the chemistry reverses: metals oxidise and precipitate, gases come out of solution, and the “clean” water turns orange, black, scaly or smelly. Understanding this is the key to treating it: most borehole treatment is about controlling that oxidation deliberately, instead of letting it happen where you don’t want it.
Each one needs a specific treatment step — there is no single “borehole filter”.
Invisible in the aquifer; precipitates as orange/brown deposits on contact with air. Stains fixtures and laundry, fouls RO membranes, blocks pipework. Needs oxidation then filtration.
Fe/Mn RemovalBlack staining, harder to oxidise than iron — needs a higher pH or a catalyst. Often the parameter that defeats a simple plant. Tiny limits (0.05 mg/L potable).
Fe/Mn RemovalExcess dissolved CO₂ makes water acidic and corrosive (low Langelier index), attacking pipes and concrete. Stripped out by aeration, then pH corrected.
Aeration TowersRotten-egg smell, corrosive, toxic at the wellhead. Formed by sulphate-reducing bacteria in the aquifer. Removed by aeration/stripping and oxidation.
Aeration TowersCalcium and magnesium scale boilers, cooling systems and RO membranes. Managed by softening or antiscalant depending on end use.
Hardness & SofteningSub-micron 1–3 µm colloids pass straight through sand filters and drive the Silt Density Index that fouls RO. Needs ultrafiltration.
RO Pre-TreatmentAmmonia consumes disinfectant and feeds nitrification; nitrate breaches potable limits. Removed biologically, by ion exchange or RO.
Ammonia TreatmentEven deep boreholes can suffer ingress (E. coli, coliforms). A potable supply needs a disinfection barrier and a sampling regime.
DisinfectionCoastal or deep boreholes can be brackish. High TDS/chloride needs reverse osmosis to reach potable or process quality.
RO Pre-TreatmentIndicative figures — only a treatability assessment of your water is definitive.
| Parameter | Often found in borehole water | UK/EU potable limit | Main impact |
|---|---|---|---|
| Iron (Fe) | 0.5–15 mg/L | 0.2 mg/L | Staining, fouling |
| Manganese (Mn) | 0.1–3 mg/L | 0.05 mg/L | Black staining |
| Hardness | 150–500 mg/L CaCO₃ | (indicator) | Scaling |
| Ammonium | 0–3 mg/L | 0.5 mg/L | Disinfection demand |
| Nitrate | 0–100 mg/L | 50 mg/L | Health limit |
| Turbidity | 0.5–20 NTU | 4 NTU (1 at works) | RO fouling, aesthetics |
| H₂S | 0–5 mg/L | none detectable | Odour, corrosion |
The complete treatment train and how to choose it.
Read MoreRemoves Fe, Mn, CO₂ and H₂S — the first step.
Read MoreWhy borehole plants under-perform — and how to avoid it.
Read MoreTest the actual water before designing the plant.
Read MoreSend us a water analysis — or let us sample it — and we will identify exactly which of these problems you have, what each one will cost you untreated, and the treatment train that fixes them.
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