A global journey focusing on water’s widespread role across the planet begins in Banjul, The Gambia, at 07:00 UTC. This expedition notes water’s fundamental importance, from its physiological presence in living organisms to its key function in global commerce and natural systems. The journey concludes back in Banjul after covering 69,570km (43,229 miles) over 24 hours. The annual renewable water resource of The Gambia itself stands at 8 billion m³.
Water constitutes an average of 60% of adult males by weight and 55% of adult females. The Earth itself holds approximately 1.4 billion km3 of water, showing its abundance. Beyond its biological and environmental significance, seas facilitate roughly 80% of world trade by volume, demonstrating water's integral role in economic activity.
The Ocean's Vast Influence
Seas cover 71% of the Earth’s surface. The Atlantic Ocean plays a role in regulating global temperatures by transporting cold and warm water between the tropics and the poles. Oceans absorb approximately 90% of the excess heat trapped by greenhouse gases. These vast bodies of water also account for 86% of global evaporation and 78% of global precipitation. The five ocean basins collectively hold 1.3 billion Km³ of salt water, representing 97% of all water on Earth. Maritime shipping relies on these oceans, moving over 80% of global trade.
Lagos, Nigeria, situated on the Gulf of Guinea, a marginal sea of the Atlantic, exemplifies a major port city connected to this global network. Further across the Pacific, Honolulu, Hawaii, serves as a point of reference, noting the global importance of fisheries. Fisheries provide livelihoods for over 600 million people and supply about 17% of global animal protein intake. However, a concerning trend shows that the proportion of fish stocks that are biologically unsustainable increased from 10% in 1974 to 34.8% in 2017. Anchorage, Alaska, further emphasizes the vastness of oceanic influence, noting Alaska has more coastline than all other US states combined. Water’s influence extends beyond oceanic trade and food sources to energy generation; Vancouver, British Columbia (BC), Canada, a leading hydroelectric region, utilizes 33 hydro plants to supply 91% of its energy needs. Globally, hydropower stands as the largest source of renewable energy, producing 14.3% of electricity generated in 2022.
Inland, water remains critical for industry and agriculture. Bogota, Colombia, is visited to illustrate industry’s use of water. Industry accounted for 7% of global freshwater withdrawals in 2014. The energy sector alone consumed 370 billion m³ (about 10%) of global freshwater withdrawals in 2021. Agricultural production, particularly for certain commodities, demands significant water resources; Caracas, Venezuela, notes agriculture as the dominant water user, consuming around 70% of global freshwater withdrawals. Beef, for instance, requires about 15,400 litres of water per kilogram to produce, while rice requires approximately 2,500 litres per kilogram. Buenos Aires, Argentina, draws attention to domestic water use, which accounts for about 10% of global freshwater withdrawals. In 2022, per person per day (PPPD) water use ranged from 21 litres in Senegal to 295 litres in the US and 380 litres in the UAE. The impact of water quality on public health is also starkly evident, with poor water, sanitation, and hygiene (WASH) contributing to the deaths of over 1 million people in 2019. Water-borne diseases tragically killed five times more people in 2020 than were killed by natural disasters and conflicts. Mexico City, Mexico, a megacity, produced an estimated 6.5 million m³ of wastewater per day in 2016. Globally, an estimated 2,212 km³ (56%) of freshwater withdrawn annually is returned as wastewater, with approximately 80% of this wastewater released to the environment without adequate treatment.
Rivers, Lakes, and Groundwater Systems
Cairo, Egypt, is situated on the banks of the Nile, which is the longest river in the world. Egypt relies on the Nile for over 90% of its water resources. Water-related conflicts are a historical concern, with over 2,700 such conflicts recorded since 2500 BC.
Nairobi, Kenya, is located above the Nairobi Aquifer System (NAS), noting the global importance of subterranean water sources. Groundwater accounts for approximately 40% of irrigation water, a third of industrial water use, and nearly half of all drinking water worldwide. The Nubian Sandstone Aquifer System (NSAS), spanning over two million Km² across Sudan, Chad, Libya, and Egypt, is the largest aquifer globally. Infiltration, the process by which water seeps into the ground, is critical to the water cycle because it helps recharge groundwater. Pago Pago, American Samoa, located on volcanic Tutuila island, illustrates a challenge where much rainfall runs off instead of infiltrating into the soil.
Karachi, Pakistan, is positioned at the edge of the Indus River Delta, demonstrating how major urban centers often develop near significant river systems. Globally, 90% of the world’s population lives within 10 Km of a river, and about 2 billion people rely on rivers for drinking water. Dhaka, Bangladesh, exemplifies this reliance, situated at the confluence of the Meghna, Brahmaputra, and Ganges rivers.
Lakes also play a significant role in freshwater availability, holding about 87% of all surface liquid freshwater in the world. These inland bodies of water support diverse ecosystems and human activities. Inland fisheries supplied 11.3 million tonnes of aquatic products in 2022, showing their contribution to global food security. Lakes support the livelihoods of an estimated 60 million people worldwide and provide 14% of global electricity through hydropower. The 21 largest lakes facilitate significant cargo movement, supporting 195 million tonnes of transport annually.
Atmospheric Moisture and Precipitation
About 496 trillion cubic meters of water evaporate from the Earth’s surface annually, predominantly from oceans, which contribute 86% of all evaporation globally. Bangkok, Thailand, is a location that shows how the atmosphere holds approximately 12.9 trillion cubic meters of water vapor, cycling every nine days on average. When billions of water vapor droplets condense simultaneously, they release enough heat to power thunderstorms with winds that can exceed 100 kilometers per hour.
Beijing, China, notes evaporation as an important driver of the water cycle. This process can lead to significant water loss from surface bodies, as seen with Egypt’s Lake Nasser, which loses 10 to 16 billion cubic meters per year. The city of Tokyo, Japan, draws attention to the role of forests, with 67% of Japan’s land area covered by them. Forests contribute significantly to global transpiration, which is the release of water vapor through plant leaves. Transpiration accounts for 10% of all atmospheric moisture and can reduce air temperature by 1 to 8 degrees Celsius.
The Amazon rainforest exemplifies this impact, where its 390 billion individual trees transpire 20 billion tonnes of water daily. Overall, evapotranspiration transfers over 60% of all precipitation back to the atmosphere. Sydney, Australia, demonstrates that condensation is a fundamental process, forming clouds, frost, dew, and fog. In arid regions such as the Atlas Mountains in Morocco and Chile’s Atacama, fog is harvested as a valuable source of freshwater.
Freshwater Storage and Distribution
Approximately 391,000 cubic kilometers (km³) of precipitation falls over oceans annually, while 111,000 km³ falls over land. Annually, 502 thousand km³ of evaporated water is returned as precipitation. Honiara, Solomon Islands, exemplifies areas receiving significant rainfall, with approximately 3,000 millimeters recorded each year. Precipitation in the Solomon Islands is largely driven by the Intertropical Convergence Zone (ITCZ). Although Earth contains about 1.4 billion km³ of water, only 2.5% of it is freshwater, predominantly stored in glaciers and polar ice caps. Around 69% of this freshwater is locked in glaciers and polar ice caps, and 30% exists as groundwater. Ice caps, glaciers, and snow collectively store about 1.7% of the 1.4 billion Km³ of water on Earth, yet they hold 68.7% of all freshwater worldwide. The amount of freshwater readily available for human use is limited to about 1%, with 87% of that located in freshwater lakes. This scarcity contributes to 1.1 billion people globally lacking access to water, with women and girls disproportionately affected.
Denver, Colorado, situated near the Rocky Mountains, notes regions where snow and ice form part of the cryosphere, which stores approximately 69% of all freshwater on Earth. Glaciers in mountain ranges provide meltwater for an estimated 2 billion people globally. Meanwhile, sea ice has been decreasing by about 13% per decade since 1979.
Water Use, Challenges, and Future
Ensuring the availability of clean water and sanitation for all by 2030 is outlined as Goal 6 of the UN’s 17 Sustainable Development Goals (SDGs). Dubai, United Arab Emirates (UAE), records the world's highest per capita water consumption, reaching 550 litres per person per day (PPPD). Beyond direct consumption, lakes globally support the livelihoods of an estimated 60 million people and contribute 14% of global electricity through hydropower. The 21 largest lakes facilitate significant cargo movement, supporting 195 million tonnes of transport annually.
A concerning trend shows that surface water bodies in 364 basins around the world are shrinking. Suva, Fiji, serves as a point of reference for water-based tourism, an industry projected to increase from $298 billion in 2024 to US$1,085 billion in 2034. Coastal areas attracted about 50% of international travellers in 2017. Apia, Samoa, is visited where 89% of Samoa’s population has piped water, but many still rely on rainwater harvesting, springs, and small reservoirs. Nuku’alofa, Tonga, frequently experiences flooding due to a high rate of rainwater runoff, which occurs when rainfall exceeds the soil’s capacity to absorb it.
The journey concludes back in Banjul after a 24-hour, 69,570km (43,229 miles) journey, showing the interconnectedness of water systems and human societies across the globe.
