Understanding your results
Water parameter library
Every result on your certificate is explained here in plain English: what the parameter is, where it comes from, why it matters, and what a Pozzani engineer can do if a result is over the guideline.
Metals 15 parameters
Lead, copper, iron, manganese and the rest. Mostly from pipework and fittings rather than the source, so the fix is usually in the plumbing.
- Aluminium µg/l A metal from soils and from some treatment chemicals. Causes discolouration; the guideline is set for appearance. Read the guide →
- Antimony µg/l A metal that can leach from some solders and fittings. Tested for new-build compliance in Scotland. Read the guide →
- Arsenic µg/l A naturally occurring element in some rocks and soils. A health parameter with a low guideline. Read the guide →
- Cadmium µg/l A toxic metal from galvanised pipework, industrial pollution and some fertilisers. Tested for new-build compliance in Scotland. Read the guide →
- Chromium µg/l An industrial metal. Rare in private supplies; tested for new-build compliance in Scotland. Read the guide →
- Cobalt µg/l A trace element plants need in tiny amounts. Measured for hydroponics; no UK drinking-water limit. Read the guide →
- Copper mg/l A metal that dissolves from copper pipework, especially in soft or acidic water. Causes blue-green staining. Read the guide →
- Iron µg/l A common metal in groundwater. Causes orange-brown staining and a metallic taste rather than any health risk. Read the guide →
- Lead µg/l A metal that gets into water from old pipes and fittings. There is no safe level, so the aim is as little as possible. Read the guide →
- Manganese µg/l A metal often found with iron. Causes black staining and a bitter taste; the guideline also reflects a health consideration at high levels. Read the guide →
- Mercury µg/l A toxic metal, rare in UK water. Tested where there is reason to suspect industrial or mining pollution. Read the guide →
- Molybdenum µg/l A trace element essential to plants for using nitrogen. Measured for hydroponics; no UK drinking-water limit. Read the guide →
- Nickel µg/l A metal that comes mainly from nickel-plated taps and fittings. Tested for new-build compliance in Scotland. Read the guide →
- Silver µg/l A metal that is rare in natural water and usually comes from silver-based filters or treatment units. Tested for new-build compliance in Scotland. Read the guide →
- Zinc µg/l A metal from galvanised pipes and brass fittings. Affects taste and appearance rather than health. Read the guide →
Bacteria 8 parameters
E. coli, coliforms, enterococci, Legionella and colony counts. For most of these the only acceptable result is none, and a fail means boil until a retest is clear.
- Clostridium perfringens (incl. spores) cfu/100ml A hardy faecal indicator whose spores survive for months. Shows contamination may have happened some time ago. Read the guide →
- Coliform bacteria cfu/100ml A family of bacteria used as a general warning sign that a supply is not properly protected or treated. Read the guide →
- Colony count 22°C cfu/ml A count of the general bacteria in the water. There is no fixed limit; what matters is a sudden change. Read the guide →
- Colony count 37°C cfu/ml A count of bacteria that grow at body temperature. Watched for change alongside the 22°C count. Read the guide →
- E. coli cfu/100ml A bacterium found in the gut of people and animals. Finding it means the water has been contaminated with faeces and is not safe to drink untreated. Read the guide →
- Enterococci cfu/100ml A second indicator of faecal contamination that survives longer in water than E. coli. Read the guide →
- Legionella spp. cfu/l Bacteria that grow in warm water systems and can cause Legionnaires' disease when inhaled in fine spray. Read the guide →
- Pseudomonas aeruginosa cfu/250ml An opportunistic bacterium that thrives in warm water, hoses and biofilm. A key check for pools, spa pools and vulnerable users. Read the guide →
Minerals and hardness 9 parameters
Calcium, magnesium, hardness, sodium, chloride, sulphate and fluoride. Natural to the ground the water came through, and the cause of limescale.
- Boron mg/l An element from natural minerals and some detergents. Tested for new-build compliance in Scotland. Read the guide →
- Calcium mg/l One of the two minerals that make water hard. Not a health concern. Read the guide →
- Chloride mg/l Dissolved salt. High levels taste salty and can point to seawater, road salt or sewage reaching the supply. Read the guide →
- Fluoride mg/l Naturally present in some groundwaters. Protects teeth at low levels; too much can mottle them. Read the guide →
- Hardness mg/l CaCO3 The amount of calcium and magnesium in the water. Causes limescale but is not a health concern. Read the guide →
- Magnesium mg/l The second hardness mineral. Not a health concern; reported so the mineral balance can be read. Read the guide →
- Silica mg/l Dissolved silica from rocks and sand. Relevant to hydroponic nutrient balance and to scale on equipment. Read the guide →
- Sodium mg/l The other half of salt. Raised naturally in some areas and by water softeners. Read the guide →
- Sulphate mg/l A natural mineral. High levels taste bitter and can have a laxative effect for people not used to them. Read the guide →
Nutrients and nitrogen 4 parameters
Nitrate, nitrite, ammonium and phosphate. Usually from farmland, septic systems or slurry near the source.
- Ammonium mg/l Also called ammonia. Usually a sign of sewage or farm waste reaching the supply, or of bacterial activity. Read the guide →
- Nitrate mg/l A nutrient that reaches water from fertilisers, manure and septic systems. Matters most for bottle-fed babies. Read the guide →
- Nitrite mg/l A short-lived form of nitrogen that signals contamination or incomplete treatment. Matters most for bottle-fed babies. Read the guide →
- Phosphate mg/l A plant nutrient. No drinking-water limit; measured for hydroponics to balance the feed. Read the guide →
Taste, smell and appearance 3 parameters
What you notice at the tap: taste, odour and cloudiness. Not usually a health risk on their own, but often the first sign of something else.
- Odour dilution number How the water smells, assessed by the laboratory. Should be acceptable with no abnormal change. Read the guide →
- Taste dilution number How the water tastes, assessed by the laboratory. Should be acceptable with no abnormal change. Read the guide →
- Turbidity NTU How cloudy the water is. Cloudiness can shield bacteria from disinfection and is often a sign of other problems. Read the guide →
Physical and chemical 3 parameters
pH, conductivity and organic carbon. The overall character of the water, and what drives corrosion and treatment choices.
- Conductivity µS/cm A quick measure of how much dissolved mineral the water carries overall. Read the guide →
- pH pH units How acidic or alkaline the water is. Low pH water is corrosive and dissolves metals from pipes. Read the guide →
- Total organic carbon mg/l A measure of all the organic matter in the water. Watched for change; high levels affect disinfection. Read the guide →
Effluent and discharge 6 parameters
The determinands a trade effluent consent sets limits on: oxygen demand, solids and dissolved matter in water leaving a site.
- Biochemical oxygen demand (BOD, 5 day + ATU) mg/l How much oxygen bacteria use to break down what is in your effluent. The single figure most trade effluent consents are built around. Read the guide →
- Chemical oxygen demand (COD) mg/l The oxygen needed to chemically oxidise everything in the effluent. A faster, broader measure than BOD, used alongside it. Read the guide →
- Settleable solids (1 hour) mg/l The solids that drop out of the effluent within an hour. What a settlement tank or interceptor would catch. Read the guide →
- Suspended solids after 1 hour settlement mg/l The solids still in suspension after the sample has stood for an hour. Shows what a settlement tank would leave behind. Read the guide →
- Total dissolved solids (180 °C) mg/l Everything dissolved in the effluent, weighed after the water is dried off. Salts, minerals and dissolved process chemicals. Read the guide →
- Total suspended solids mg/l The solid matter carried in the effluent, by weight. Charged for by the water company and a common reason for a consent breach. Read the guide →