How does water move through the environment, and how is it managed as a resource?
The hydrosphere: the water cycle and the distribution of water, water as a resource, the causes and effects of water pollution, and the treatment of water for supply and after use.
An SQA Higher Environmental Science answer on the hydrosphere, covering the water cycle and the distribution of fresh water, water as a resource, the causes and effects of water pollution including eutrophication, and how water is treated for supply and after use.
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What this dot point is asking
The SQA wants you to describe the hydrosphere: the water cycle and how water is distributed on Earth, water as a resource, the causes and effects of water pollution (especially eutrophication), and how water is treated both for supply and after use. This is the water sphere of the Earth's Resources area.
The water cycle and the distribution of water
Water is driven round the water cycle by the Sun and gravity: evaporation (and transpiration from plants) lifts water vapour into the air, condensation forms clouds, precipitation returns water as rain or snow, and that water then moves by surface run-off, infiltration into the ground and flow back to the sea. The cycle continually purifies and redistributes fresh water.
Water as a resource
Fresh water is essential for drinking, sanitation, agriculture (irrigation), industry and energy. Demand is rising with population and development, while supply is uneven in space and time, so water can be scarce in many regions even though the planet has plenty overall. This unequal, limited supply links directly to the sustainability of water use studied later in the course.
Water pollution: causes and effects
Water pollution lowers water quality and harms ecosystems and human health. Major causes include:
- Sewage and organic waste, which add nutrients and pathogens and lower oxygen as they decompose;
- Fertiliser and slurry run-off from farmland, which causes eutrophication;
- Industrial discharge of toxic chemicals and heavy metals, which can bioaccumulate;
- Thermal pollution, where warm water from power stations lowers dissolved oxygen and stresses organisms.
Eutrophication is the key process to know: excess nutrients trigger an algal bloom that blocks light, the algae and plants then die, and decomposer bacteria multiply and use up the dissolved oxygen, so fish and invertebrates suffocate and biodiversity falls.
Treatment of water
Drinking-water treatment makes raw water safe to supply, typically by screening out large debris, sedimentation and filtration to remove suspended solids, and disinfection (for example with chlorine) to kill pathogens.
Waste-water (sewage) treatment cleans water after use before it is returned to rivers or the sea: primary treatment settles out solids, secondary treatment uses microorganisms to break down dissolved organic matter (lowering the oxygen demand), and treatment may continue to remove nutrients. Treating waste water reduces the organic and nutrient load on rivers, helping to prevent eutrophication.
Examples in context
Example 1. Loch eutrophication from agriculture. Lochs receiving fertiliser and slurry run-off from surrounding farmland develop summer algal blooms, including toxic blue-green algae, that close the water to recreation and kill fish as oxygen falls. It shows the eutrophication sequence operating in a real Scottish freshwater body and why nutrient run-off is controlled.
Example 2. Cape Town's "Day Zero" water crisis. A multi-year drought in the 2010s nearly emptied Cape Town's reservoirs, forcing severe rationing and showing how a city can run short of fresh water even on a water-covered planet. It illustrates that accessible fresh water is limited in space and time and must be managed carefully.
Try this
Q1. Name the four main processes of the water cycle. [2 marks]
- Cue. Evaporation, condensation, precipitation, and run-off or infiltration.
Q2. State one cause of eutrophication and its first visible effect on a lake. [2 marks]
- Cue. Fertiliser run-off adds nutrients; the first visible effect is an algal bloom on the surface.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA Higher specimen4 marksDescribe the process of eutrophication that follows fertiliser run-off into a lake, and explain its effect on aquatic organisms.Show worked answer →
A 4-mark answer needs the sequence and the oxygen link to organisms.
Fertiliser run-off adds excess nutrients (nitrates and phosphates) to the water. These nutrients cause a rapid growth of algae, an algal bloom, which covers the surface.
The bloom blocks light, so plants below die. When the algae and plants die, decomposer bacteria break them down and multiply, using up the dissolved oxygen in the water.
The fall in dissolved oxygen means fish and invertebrates cannot respire, so they die. This loss of aquatic organisms reduces biodiversity.
Markers reward nutrient enrichment, the algal bloom and light blocking, decomposers using oxygen, and the death of organisms from low oxygen.
SQA Higher specimen3 marksExplain why only a very small proportion of the water on Earth is available as fresh water for human use.Show worked answer →
This is a 3-mark explain answer about water distribution.
The great majority of water on Earth, about 97 percent, is salt water in the oceans and is not directly usable for drinking or most agriculture.
Of the small remaining fresh water, most is locked up in ice caps, glaciers and deep groundwater, which are difficult or impossible to access.
Only a tiny fraction, found in accessible rivers, lakes and shallow groundwater, is readily available for human use, which is why water can be scarce despite being abundant overall.
Markers reward the dominance of salt water, fresh water being locked in ice and deep groundwater, and the small accessible fraction left.
Related dot points
- The geosphere: the structure of the Earth, the rock cycle and rock types, the formation and properties of soil, weathering and erosion, and the extraction and sustainable use of mineral resources.
An SQA Higher Environmental Science answer on the geosphere, covering the structure of the Earth, the rock cycle and the three rock types, soil formation and properties, weathering and erosion, and the extraction and sustainable use of minerals.
- The biosphere: biomes and their distribution, biological and biomass resources, the ecosystem services the biosphere provides, and the sustainable management of biological resources.
An SQA Higher Environmental Science answer on the biosphere, covering biomes and what determines their distribution, biological and biomass resources, the ecosystem services provided by living systems, and the sustainable management of biological resources such as forests and fisheries.
- The atmosphere: its composition and layered structure, its role in weather and climate, the greenhouse effect, and the causes and effects of atmospheric pollution including acid rain and ozone depletion.
An SQA Higher Environmental Science answer on the atmosphere, covering its composition and layered structure, its role in weather and climate, the natural greenhouse effect, and atmospheric pollution including acid rain and ozone depletion.
- Water: the demand for water and the causes of water scarcity, the uneven supply of fresh water, and sustainable approaches to managing and supplying water.
An SQA Higher Environmental Science answer on water as a sustainability challenge, covering the demand for water, the causes of physical and economic water scarcity, the uneven supply of fresh water, and sustainable approaches to managing and supplying it.
- Human influences on biodiversity: habitat loss and fragmentation, overexploitation, the impact of invasive non-native species, pollution, and the methods used to conserve and protect biodiversity.
An SQA Higher Environmental Science answer on human influences on biodiversity, covering habitat loss and fragmentation, overexploitation, invasive non-native species, pollution, and conservation methods such as protected areas, captive breeding and legislation.
Sources & how we know this
- Higher Environmental Science Course Specification (C826 76) — SQA (2021)
- Higher Environmental Science course overview and resources — Qualifications Scotland (2026)