World Population Day: Saving Energy and Water in a Growing World

Every year on July 11, we reflect on one of humanity’s most significant challenges - and opportunities - our growing population. World Population Day was first observed in 1990, after the United Nations Development Programme (UNDP) sparked global interest with The Day of Five Billion on July 11, 1987. This milestone date marked the moment the world population was estimated to have reached five billion people. In response, the United Nations General Assembly officially endorsed the observance to raise awareness about population trends and their impacts on health, education, gender equality, resources, and the environment. What began in over 90 countries has grown into an annual event recognized by governments, schools, and organizations around the globe.

Why It Matters for Energy and Sustainability

For most of human history, population growth was slow and steady. But advances in medicine, agriculture, and technology triggered a rapid rise over the past century. Today, our global population has surpassed 8 billion and continues to climb, with much of this growth taking place in urban areas. Urbanization brings opportunity, but it also puts pressure on energy, water, housing, transportation, and food systems. More people means more demand, and without careful planning, this can lead to resource depletion, pollution, and other heightened risks.

Population growth is directly linked to how we produce, use, and conserve resources. As economies expand, energy and water usage often rise as well. This can strain infrastructure, contribute to greenhouse gas emissions, and challenge energy security. Addressing these issues requires both innovative solutions and public understanding. By gaining more awareness of the connections between population trends, resource use, and environmental change, we can empower the next generation to create a more sustainable future.

Bringing the Conversation Into Your Classroom

World Population Day is a perfect opportunity to start these conversations, but you don’t have to stop there. Population, energy, and sustainability are interconnected issues that deserve attention year-round. Browse free lesson plans on the Watt Watchers of Texas website, including activities like Modeling Population Growth, and lead classroom discussions on how tomorrow is shaped by the choices we make today.

Featured Activity: Modeling Population Growth 

Activity: Modeling Population Growth Grade Level: High School Theme: Electricity, Water Activity Overview: The key underlying demographic trends that strain energy and water resources are population growth and economic growth. Other key trends are the impacts of global climate change and policy choices, whereby policy makers push for more water-intensive energy and more energy-intensive water. As the population increases, more people demand more energy and water. However, because of economic growth, which happens in parallel, the demand for energy and water increases faster than the population.1 This phenomenon occurs because economically affluent populations tend to consume more energy and water per person than poorer populations. Problem Statement: Describe the nature of exponential growth in human populations.  Project Deliverables: Students should use technology to research global historical estimates and population records. They should then create a mathematical model based on the data. Many population curves exist online, but students should not copy and paste them for the purpose of this assignment.  After creating their models, students should compare them with the widely accepted population curves to see how well they have modeled historical population trends. Historical data will not allow for the creation of predictions of the future, but many of the population curves will contain future predictions based on possible trajectories for population growth. Supplemental Video: The short video below, Urban Metabolism from Power Trip: The Story of Energy, illustrates how cities operate much like living organisms, consuming resources such as food, water, and energy, and producing waste. As our global population continues to grow, particularly in urban areas, this “metabolism” becomes more complex and resource-intensive. By understanding the flows of energy and water in our communities, we can better manage the impacts of population growth and design more sustainable cities. Discussion Prompt: After watching, consider how your own city’s “metabolism” might change as the population increases. What steps could be taken - locally or globally - to make this system more sustainable? Additional Resources: