Glossary

The following provides a description of common terms that may be useful when understanding private supply.

• Absorption The process by which one substance is taken into the body of another substance, called the absorbent. An example is the absorption of water into soil.
• Acid A substance which in solution produces hydrogen ions (H+), the concentration of which is expressed in terms of pH units.
• Acidic Having a pH value less than 7.
• Acidity A measure of the capacity of a solution to neutralise alkali.
• Activated carbon A family of carbonaceous substances manufactured by processes that develop adsorptive properties. Sometimes called “activated charcoal‟.
• Adsorption The process by which one substance is taken onto the surface of another substance by physical and/or chemical forces.
• Aeration The vigorous exposure of water to a stream of air bubbles. This process may increase pH by stripping carbon dioxide, remove odour-producing compounds and will increase the dissolved oxygen concentration to facilitate oxidation reactions (e.g. oxidation of iron).
• Algae Microscopic planktonic plant forms . Substantial growths (“blooms”) may be observed in nutrient-rich waters during the summer.
• Alkali Any highly basic substance, for example, hydroxides and carbonates of alkali metals such as sodium and potassium.
• Alkaline Having a pH value greater than 7.
• Alkalinity A measure of the capacity of a solution to neutralise acid. Note that there is a distinction between “alkaline” and “alkalinity” e.g. a water of acid pH (i.e. not alkaline) may contain amounts of carbonate/bicarbonate which result in a degree of alkalinity.
• Anoxic Water depleted of dissolved oxygen.
• Aquifer A porous rock which holds and transmits water.
• Bacteria Unicellular micro-organisms that typically reproduce by cell division. Many bacteria are disease-producing.
• Baffle A slat, plate or plank used in a tank to alter the flow of water in order to avoid short-circuiting, e.g. in a tank. Note that in other contexts, baffles can be used to promote mixing.
• Base Any chemical species capable of reacting with hydrogen ions.
• Base exchange A softening process using cation exchange resin to replace calcium and magnesium ions in the water with sodium ions.
• Breakpoint chlorination A method of chlorination in which a sufficient dose of chlorine is added to rapidly oxidise all of the ammonia in the water and leave a free chlorine residual.
• Buffering capacity The capacity of a water to resist pH change. This is closely related to alkalinity.
• Chloramines Compounds formed from the reaction of chlorine with ammonia, successively replacing hydrogen atoms with chlorine atoms to produce monochloramine and dichloramine (and nitrogen trichloride if the pH is low and the chlorine:ammonia ratio is very high). Chloramines are less efficient disinfectants than chlorine itself but are more persistent.
• Chlorination A process for disinfection of water using chlorine, sodium hypochlorite or calcium hypochlorite.
• Chlorine A gas (Cl₂) widely used in disinfection and oxidation processes.
• Coagulation A process for turbidity and colour removal in which a coagulant (typically aluminium sulphate or ferric sulphate) is added to the water, causing colloidal turbidity-causing material and dissolved coloured substances to agglomerate into a precipitate („floc‟) which is subsequently removed e.g. by sedimentation and/or filtration.
• Coliform bacteria A group of bacteria found in vast numbers in human excreta. Their presence in water is an indication of potential faecal contamination; consequently they are used as indicator organisms. See Escherichia coli.
• Colloid A state of matter consisting of very finely divided (less than 1 micrometer) particles suspended in a fluid, e.g. water. Although the particles are not dissolved they are too small to settle at any meaningful rate.
• Colour The shade or tint imparted to water, typically by organic substances in solution.
• Combined available chlorine The total concentration of chloramines and any organic nitrogen chlorine containing compounds. Combined chlorine is a less effective disinfectant than free chlorine.
• Contaminant Any undesirable physical, chemical, or microbiological substance in water.
• Control Measure/Corrective actions. Any action and activity that can be used to prevent or eliminate a water safety hazard or reduce it to an acceptable level. For example, chlorination of a water supply system.
• Cryptosporidium A protozoan parasite which causes acute diarrhoeal disease in humans. The organism can be transmitted by contaminated water; both surface and groundwaters may be contaminated by the cyst stage of Cryptosporidium, known as oocysts.
• Cyst A capsule associated with a dormant stage of reproduction in micro-organisms. See oocyst.
• Denitrification The reduction of nitrate to nitrogen gas. Biological denitrification is a process in which reduction is brought about by naturally occurring bacteria.
• Desalination The removal of dissolved salts (mainly sodium chloride) from sea water or brackish water to render it potable.
• Disinfection The removal, destruction or inactivation of pathogenic organisms in water.
• Emergency Planning. A process that consists of determining the response and recovery strategies to be implemented during and after emergencies.
• Escherichia coli The most abundant coliform organism present in the human and animal gut. The presence of E. coli in a water sample indicates potentially dangerous contamination of human or animal origin – see also coliform bacteria and indicator organism.
• Filter A unit for carrying out the process of filtration which consists of a combination of filter medium and a suitable holder for constraining and supporting the medium in the path of the water.
• Filtration The passage of water containing particles through a filter to effect a separation of particles from the water.
• Flocculation A term often used interchangeably with coagulation, it refers to the process by which particles are agglomerated to form flocs (see coagulation).
• Flotation A process for separating flocs from water. A recycled sidestream of water saturated with air under pressure is injected into the water. Microscopic air bubbles form at the point of injection, attach to the flocs and cause them to float to the surface where the accumulated solids can be removed.
• Free available chlorine The total concentration of free chlorine, hypochlorous acid and hypochlorite ion in water.
• Gravel filter A coarse filter for rapid filtration, consisting of a bed of gravel graded from coarse at the inlet to fine at the outlet.
• Hardness Water hardness is caused by dissolved salts such as those of calcium and magnesium. Hard waters are associated with scale formation and increased use of soap; conversely soft waters are often acidic and corrosive. See total, permanent and temporary hardness.
• A Hazard is any biological, chemical, physical or radiological agent that has the potential to cause harm.
• A hazardous event is an incident or situation that can lead to the presence of a hazard (what can happen and how).
• Hazen units (°H) An arbitrary unit for expressing the colour of water; it can be represented as the platinum-cobalt (Pt-Co) scale in which colour is expressed in mg/l Pt.
• Hypochlorite The hypochlorite ion (OCl^–) is one of the ionic species formed when chlorine is added to water. The term “hypochlorite” is also used to refer to sodium hypochlorite, another chemical used for chlorination.
• Hypochlorous acid (HOCl) is one of the species formed when chlorine is added to water.
• Indicator organism As it would be futile and impractical to screen water samples for all possible pathogenic organisms. Escherichia coli and other coliform bacteria are therefore monitored as indicator organisms; their presence in a water sample would be indicative of faecal contamination and the potential presence of pathogenic organisms in water.
• Ion An atom or group of combined atoms which has lost (or gained) one or more electrons to become a positively charged cation (or negatively charged anion).
• Ion-exchange A process in which ions of like charge are exchanged between the water phase and the solid resin phase.
• Ion-exchange resin A synthetic organic ion-exchange material, used for example in ion-exchange softeners and nitrate removal units. Typical resins are in the form of small beads.
• Local authority means any of the following; the Common Council of the City of London; a London borough council; a district council; or the council of a county in which there are no district councils.
• Marginal (simple) chlorination The usual chlorination technique employed for small supplies of high quality. It is simply the dosing of sufficient chlorine to produce a suitable free chlorine residual.
• Membrane A semi-permeable barrier that allows passage of water but not dissolved substances. Commonly used membranes are made of cellulose acetate and polyamides.
• Microfiltration A pressure-driven membrane process using a membrane with pore size in the range 0.05 to 2 µm to separate suspended and colloidal material.
• µg/l microgram per litre (one millionth of a gram per litre)
• Micrometre (µm) A linear measure equal to one millionth of a metre; also called a micron (µ).
• Microstrainer A type of filter for removing mineral and biological solids, consisting of a rotating drum fitted with fine mesh panels. Water washing is used to remove accumulated debris.
• Milligram per litre (mg/l) A unit of concentration used in reporting analytical results. For practical purposes it is the same as ppm (parts per million).
• Mitigation. All actions taken to reduce or eliminate long term risk to environmental health or social structures from hazards and their effect.
• Molecule The smallest particle into which a compound may be divided and still retain the essential composition and properties of that compound. Molecules are composed of the atoms of individual elements.
• Nanofiltration A pressure-driven process using a membrane with properties intermediate between reverse osmosis and ultrafiltration membranes. Nanofiltration membranes allow monovalent ions (e.g. sodium) to pass but selectively remove divalent ions (e.g. calcium).
• Nephelometer An instrument used to measure turbidity of water. A nephelometer measures the amount of light scattered by suspended particles.
• Nitrification The oxidation of ammonia to nitrite and nitrate. Biological nitrification is a process in which the oxidation is brought about by naturally occurring bacteria.
• NTU Nephelometric Turbidity Unit. An arbitrary unit for expressing turbidity measured using a nephelometer. Also commonly used, closely related and practically numerically equivalent are Formazin Turbidity Unit (FTU) and Jackson Turbidity Unit (JTU)
• Oocyst The dormant encysted form of a protozoan parasite such as Cryptosporidium. The oocyst is the environmentally stable, infective, form of the parasite.
• Oxidation A chemical reaction in which the oxygen content of a compound is increased or in which a compound or ion loses electrons, thereby increasing its positive valency state (e.g. oxidation of ferrous to ferric iron).
• Ozonation A process used for oxidation and disinfection using ozone.
• Ozone A gas (O₃) used as an oxidant and disinfectant in water treatment. Ozone is generated at the point-of-use using an ozoniser that employs high voltage electrical discharge through air or oxygen to produce ozone at a concentration of a few percent in the feed gas.
• Pathogen A disease causing organism.
• Parameter is a numerical or other measurable factor forming one of a set that defines a system. For example the properties, elements, organisms or substances listed in the first column of the Tables in Schedule 1 in the Private Supply Regulations.
• Peak demand The maximum momentary load (maximum water flowrate) placed on a water supply system. Domestic peak demand can be as great as 3 times the average daily demand.
• Permanent hardness Hardness which is not precipitated by boiling. It is due to the presence of the chlorides and sulphates of calcium and magnesium.
• pH value A logarithmic measure of acid or alkaline nature. pH 7 is neutral, acid solutions have a pH less than 7, alkaline more than 7. Each successive pH unit represents a tenfold change in acid or alkaline nature.
• Plumbosolvency The contamination of water by lead resulting from dissolution of corrosion products from lead pipes and lead-containing solders or fittings.
• Point-of-entry A term referring to the treatment of the entire supply of water delivered to or entering buildings or properties.
• Point-of-use A term referring to treatment of water for drinking at the pointof- use or immediately prior to the point of delivery, i.e. typically at the kitchen tap, using for example a plumbed-in unit or system.
• Prescribed concentration or value (PCV) is the numerical value assigned to public drinking water standards defining the maximal or minimal legal concentration or value of a parameter.
• Pressure filter A type of filter consisting of graded sand layers contained within a closed steel vessel, through which water is passed under pressure.
• Private supply Any water supply which is not provided by a statutory water undertaker.
• Protozoa Animal or vegetable organisms that consist of a single cell and which reproduce by fission. Most are microscopic, aquatic, and some are parasites.
• Rapid sand filter Otherwise known as a rapid gravity filter, this consists of a bed of sand or other filtration medium contained in a concrete or steel vessel, through which water passes downwards by gravity.
• Relevant person means any or all of the following:
  • The owner and the occupier (who may be the same or different persons) of premises (land and any buildings on it), which are supplied with water for domestic or food production purposes by means of a private supply;
  • The owner and the occupier (who may be the same or different persons) of land on which any part of the supply is situated;
  • Any other person who exercises powers of management or control in relation to that supply.
• Reverse osmosis A pressure-driven membrane process using a membrane with pore size below 0.002 µm to remove dissolved salts and organic compounds.
• Risk is the likelihood of identified hazards causing harm in exposed populations in a specified timeframe, including the magnitude of that harm and/or the consequences.
• Risk assessment is a review undertaken to identify actual or potential hazards to human health in a water treatment works and associated supply system. Prioritisation of risk is based on consideration of likelihood and consequence of the risk occurring.
• Risk Management. Decision-making process involving considerations of political, social, economic, and technical factors with relevant risk assessment information relating to a hazard so as to develop, analyse, and compare regulatory and non-regulatory options and to select and implement appropriate regulatory response to that hazard. Risk management comprises three elements: risk evaluation; emission and exposure control; and risk monitoring. The process of evaluating alternative actions, selecting options and implementing them in response to risk assessments.
• Risk monitoring. Process of following up the decisions and actions within risk management in order to ascertain that risk containment or reduction with respect to a particular hazard is assured. Risk monitoring is an element of risk management.
• Sedimentation A process for removing suspended solids by passing water slowly and evenly through a lagoon, channel or tank to allow sediment to settle. Many different types of sedimentation system exist. Accumulated solids are removed periodically by appropriate mechanical or manual means.
• Slow sand filter This consists of a layer of fine sand supported by a layer of gravel with a system of underdrains. Water is passed downwards at a low flowrate and solids accumulate at the sand surface, forming a biologically-active layer. Impurities are removed both by physical straining and biological action.
• Softening Reduction of hardness (calcium and magnesium) by precipitation (lime or lime-soda softening) or ion-exchange (base exchange softening). Water conditioners which dose polyphosphates modify the hardness compounds, preventing them from precipitating and forming scale, but do not actually soften the water in the sense of removing calcium and magnesium.
• Superchlorination/ dechlorination A chlorination process involving the addition of a large dose of chlorine to effect rapid disinfection and chemical reaction. This is followed by a dechlorination stage using e.g. sulphur dioxide or sodium bisulphite to reduce the excess free chlorine residual.
• Temporary hardness Hardness which is precipitated by boiling. It is due to the presence of calcium and magnesium bicarbonate.
• Total hardness A measure of the total amount of calcium and magnesium in solution. Total hardness is equal to the sum of permanent and temporary hardness.
• Trihalomethanes A group of organic chemicals, including chloroform, which are formed in low concentrations during chlorination of waters containing natural organic compounds, such as the coloured humic and fulvic acids.
• Turbidity An optical property of water resulting from the scattering of light by suspended and colloidal particles. Turbidity is determined using a nephelometer and the results give a measure of the amount of particulate matter present.
• Ultraviolet (UV) irradiation A disinfection process using a mercury discharge lamp to irradiate the water, contained in a suitable chamber, with UVC radiation in order to inactivate micro-organisms.
• Validation involves obtaining evidence that the elements of the water safety plan are effective.
• Verification. The application of methods, procedures, tests and other evaluations, to determine compliance with the Water Safety Plan. The application of methods, procedures, tests and other evaluations, in addition to monitoring, to determine compliance.
• Verification monitoring. The application of methods, procedures, tests and other evaluations, in addition to those used in operational monitoring, to determine compliance with the system design parameters and/or whether the system meets specified requirements (e.g. microbial water quality testing for E. coli or helminth eggs, microbial or chemical analysis of irrigated crops).
• Virus A sub-microscopic infective agent which may be a living organism or a complex protein capable of living in cells. Viruses cause a number of diseases in animals and plants.
• Water Safety Plan (WSP) is the most effective way of ensuring that a water supply is safe for human consumption and that it meets the health based standards and other regulatory requirements. It is based on a comprehensive risk assessment and risk management approach to all the steps in a water supply chain from catchment to consumer. More information is available here.