Glossary Terms

The build-up of acidity in soils, lakes and forests caused mainly by sulphur dioxide, nitrogen oxides and ammonia, which return to the ground in rain or as deposits. It harms…

Two ways of building a life cycle model, suited to different questions. An attributional model describes the share of the world's impacts that belongs to a product, using average data.…

Not this project: an established LCA characterisation method called AWARE, short for Available WAter REmaining, developed by the WULCA working group of the UNEP Life Cycle Initiative. It weights water…

CAPEX is the upfront investment -- building the plant, membranes, pumps, pipes. OPEX is the running cost -- energy, chemicals, staff, maintenance, sludge disposal. Water reuse technologies often trade one…

The total greenhouse gas emissions and removals over a product's life cycle, expressed in CO₂ equivalent, standardised for products in ISO 14067. It is an LCA restricted to a single…

A number expressing how much a unit of a given flow contributes to an impact category, relative to a reference substance. In climate change, for example, 1 kg of methane…

A model of production and consumption that keeps materials and products in use for as long as possible through sharing, leasing, reuse, repair, refurbishment and recycling, in contrast to the…

Outputs of the same process that each have value. A co-product is one of several outputs that justify running the process; a by-product is a secondary output that arises anyway…

An appraisal that compares all the costs and benefits of an option in monetary terms, including external ones, to decide whether society is better off with it. Where LCC asks…

A study scope that follows a product through its entire life cycle, from resource extraction to final disposal. Narrower scopes are common: cradle-to-gate stops when the product leaves the factory,…

An independent check that an LCA follows the relevant standards and that its methods, data and interpretation are sound and transparent. Under ISO 14044 it is mandatory, by a panel…

Rules stating which small flows may be left out of a study -- for instance any input contributing less than 1% of total mass or energy. They keep data collection…

How fit the data used in a study are for its goal, judged on criteria such as time, geographical and technological representativeness, precision, completeness and consistency. Inconsistent data quality is…

A measure of health damage that adds up years of life lost to premature death and years lived with illness or disability, weighted by severity. LCIA methods use it as…

Converting future costs and revenues into their present value, reflecting that money spent or earned later is worth less than money today. The discount rate chosen can decide whether a…

The ratio between the value a product or system delivers and the environmental impact it causes -- more value per unit of impact, or less impact per unit of value.…

A material or energy flow that crosses the boundary between the technical system and the environment without further human transformation: water abstracted from a river, carbon dioxide released to air,…

The final stage of a life cycle, describing what happens to a product or its parts once it is no longer used: reuse, recycling, recovery of energy or materials, incineration…

The European Commission's harmonised LCA methods for products (Product Environmental Footprint) and organisations (Organisation Environmental Footprint), set out in Commission Recommendation (EU) 2021/2279. They fix many choices ISO leaves open…

A standardised, independently verified document reporting the life cycle environmental performance of a product, following ISO 14025. EPDs are built on Product Category Rules (PCRs), which fix how products in…

Over-enrichment of water bodies with nutrients -- mainly nitrogen and phosphorus -- leading to algal blooms, oxygen depletion and loss of aquatic life. It is one of the impact categories…

Costs or benefits that fall on third parties or the environment and are not reflected in market prices -- pollution damage, or the value of freshwater left in a river.…

Foreground data describe the processes a study is directly about and can measure -- the energy meter and chemical dosing records of a specific treatment plant. Background data describe generic…

The quantified function a system delivers, used as the reference to which every input, output and impact is related -- for example the production of 1 m³ of reclaimed water…

The climate change indicator in most LCAs, expressing all greenhouse gas emissions as the amount of carbon dioxide that would cause the same warming, usually over 100 years (GWP100). In…

The first phase of an LCA, where the study's purpose, intended audience and ground rules are fixed: the functional unit, the system boundary, the impact categories to be assessed, allocation…

Domestic wastewater from sinks, showers, baths and washing machines, excluding toilet wastewater (blackwater). Being less contaminated, it can be treated locally with simpler systems -- such as the experimental green…

A screening step that identifies the life cycle stages, processes or flows responsible for most of a product's impacts. It tells practitioners where better data are most needed and tells…

Impact categories for the harm that chemicals released along the life cycle cause to people (human toxicity) and to freshwater, marine and soil organisms (ecotoxicity). Heavy metals and micropollutants in…

An environmental issue an LCA reports on, such as climate change, freshwater eutrophication, acidification, human toxicity, ecotoxicity, resource depletion or water use. Reporting several categories rather than one is deliberate:…

In S-LCA, a specific social issue assessed for a stakeholder category -- for example health and safety, fair salary or working hours for workers; access to material resources, safe and…

Long-lived assets used to deliver a product rather than consumed by it: buildings, tanks, pipes, pumps, membranes. Many LCAs leave them out on the grounds that their impact, spread over…

The final phase of an LCA, where results are checked for completeness, sensitivity and consistency, and turned into conclusions, limitations and recommendations that match the study's goal. Good interpretation says…

An impact category for the occupation and transformation of land and the resulting loss of soil quality and habitat. It matters for comparing compact technologies with land-hungry ones such as…

A packaged set of impact categories, characterisation models and factors -- and sometimes normalisation and weighting sets -- used to carry out impact assessment consistently. Widely used examples are the…

The consecutive and interlinked stages of a product system, from raw material acquisition or generation from natural resources to final disposal. For a water reuse scheme this typically spans construction…

A method for quantifying the environmental impacts of a product or system across its whole life cycle, standardised in ISO 14040 and ISO 14044. A study runs through four phases:…

A method for totting up all the costs of a product or system over its life span: investment, operation, maintenance, energy, chemicals, and end-of-life, and where relevant the revenue from…

The third phase of an LCA, which translates the inventory's long list of flows into a short set of environmental impact indicators. Each flow is assigned to the impact categories…

The second phase of an LCA: compiling every input and output of the system per functional unit -- energy, chemicals, materials, water, emissions to air, water and soil, and waste.…

A curated collection of datasets describing common processes -- electricity generation, chemical production, transport, waste treatment -- that practitioners use to model the background of their systems. ecoinvent, maintained by…

Using life cycle thinking in everyday business and policy decisions -- in product design, procurement, investment and strategy -- so that environmental and socio-economic burdens are reduced across the whole…

The combination of LCA, LCC and S-LCA into one assessment covering the environmental, economic and social dimensions of sustainability. The three must share the same product system, boundaries and functional…

The habit of judging a product, service or process by everything it causes over its whole life -- from extracting raw materials, through manufacture, use and maintenance, to disposal or…

A wastewater treatment technology that combines biological treatment with membrane filtration, producing high-quality effluent suitable for demanding reuse. It is compact but energy-intensive. Two AWARE study cases use it: the…

Two levels at which impacts can be reported. Midpoint indicators sit early in the cause-effect chain -- kg CO₂ equivalent, kg phosphorus equivalent -- and are relatively certain. Endpoint indicators…

Expressing environmental or social impacts in money so they can be weighed directly against financial costs. Common routes are willingness to pay (what people would give up to obtain an…

A family of methods for choosing between options when several criteria that cannot be reduced to one unit matter at once -- environmental, economic and social results, for instance. It…

Many processes produce more than one useful output: a wastewater plant delivers clean effluent and may also yield biogas, sludge for agriculture or recovered nutrients. Allocation is the rule for…

The sum of all discounted costs and revenues over a project's life. A positive NPV means the discounted benefits outweigh the discounted costs. In LCC it is the usual single…

Optional steps after characterisation. Normalisation expresses each indicator relative to a reference -- such as the average annual impact of one person -- to show which results are large in…

The thinning of the stratospheric ozone layer, which shields the Earth from ultraviolet radiation, by substances such as CFCs and some refrigerants, expressed in CFC-11 equivalent. Thanks to the Montreal…

An impact category for the health damage caused by fine particles in the air, emitted directly or formed from gases such as sulphur dioxide, nitrogen oxides and ammonia. It is…

The formation of ground-level ozone -- summer smog -- when nitrogen oxides and volatile organic compounds react in sunlight. Ozone at ground level irritates the lungs and damages crops, unlike…

Primary data are measured or calculated directly from the process being studied -- meter readings, dosing logs, lab analyses of effluent quality. Secondary data come from elsewhere: databases, literature, industry…

The set of connected processes, linked by flows of products and services, that together deliver the function being studied. For a water reuse scheme it includes the treatment plant, but…

Wastewater that has been treated to a quality suitable for a specified reuse, such as agricultural irrigation or urban non-potable uses. The treatment needed -- and so the environmental and…

The amount of product or service needed to deliver one functional unit. If the functional unit is 1 m³ of reclaimed water for irrigation, the reference flow of a plant…

An S-LCA technique for turning qualitative social information into scores. Each indicator is rated on an ordinal scale -- typically from well below to well above an expected level of…

Impact categories for the depletion of non-renewable resources: fossil fuels, expressed as energy content, and minerals and metals, expressed relative to a reference element. Water is usually treated in its…

A membrane process that forces water through a semi-permeable membrane under high pressure, removing dissolved salts and most other contaminants. It produces very pure water for industrial reuse, at the…

Testing how much the results change when an assumption, a data point or a methodological choice is varied -- a different electricity mix, a different allocation rule, a longer plant…

The degree to which users, residents and decision-makers are willing to accept a technology or intervention. For water reuse it is often the deciding factor -- technically sound schemes have…

A stage, activity or location in a life cycle where there is a high risk of adverse social impacts, or a notable opportunity for positive ones. Hotspot screening, often with…

A method for assessing the social and socio-economic effects of a product or system on the people touched by its life cycle: workers, local communities, consumers, value chain actors, society…

In S-LCA, a group of people who share an interest in the system being assessed. The UNEP 2020 Guidelines name six: workers, local community, value chain actors, consumers, society and…

Development that meets the needs of people today without compromising the ability of future generations to meet theirs, in the sense set out by the Brundtland Commission in 1987. It…

The line that decides which processes are included in a study and which are left out. For water reuse, typical boundary questions are whether to include the sewer network, the…

A way of handling multifunctional processes by widening the system to include the products it replaces. Reclaimed water used for irrigation, for example, is credited with the freshwater abstraction and…

Quantifying how uncertain the results are, given the uncertainty in the underlying data and models, often by running the model many times with values drawn from probability ranges (Monte Carlo…

The smallest building block of a life cycle model: a single activity for which inputs and outputs are quantified, such as the aeration stage of a treatment plant or the…

Anything a process puts out that has no value -- or a negative value, meaning someone must be paid to take it away. The definition is economic, not physical: the…

A facility that removes contaminants from municipal or industrial wastewater before it is discharged or reused. Treatment is usually staged -- primary (settling), secondary (biological), and tertiary or advanced (disinfection,…

The application of circular economy principles to the water cycle, so that used water is treated as a resource -- for reuse, energy and nutrient recovery -- rather than as…

An LCA-based assessment of the potential environmental impacts related to water, standardised in ISO 14046. It can include water scarcity (how much water is consumed, and where) and water degradation…

The recovery of water, and of the energy and materials it carries, from wastewater and other used water streams, and their use again for a beneficial purpose -- irrigation, industrial…

The part of a water footprint that addresses the quantity of water consumed, weighted by how scarce water is where it is consumed. A cubic metre used in a dry…

The interdependence of these four systems: treating and moving water needs energy, producing energy and food needs water, and all of them draw on and affect ecosystems. A decision in…