Every Drop Counts: Distribution of Earth's Water & Freshwater Availability
Shared by A STEM Educator
Students will be able to describe the distribution of Earth's water (saltwater vs. freshwater, and freshwater sources) using physical models, diagrams, and data, and explain why accessible freshwater is scarce — connecting findings to real-world challenges like desalination and drip irrigation in drought-prone regions.
Lesson Overview
Students explore how Earth's water is distributed across oceans, ice caps, groundwater, and surface water using hands-on measurement, visual models, and real-world desalination and irrigation contexts. Lesson builds proportional reasoning and environmental literacy through UDL-aligned, multi-modal pathways.
Materials
- 1-liter graduated cylinders (1 per group)
- Eye droppers
- Small measuring cups (10 mL, 50 mL)
- Food coloring (blue for saltwater, clear/light blue for freshwater)
- Printed Earth's Water Distribution reference cards (see card set)
- Mini whiteboards or large sticky notes
- Pencils, colored pencils, or markers
- Printed anchor chart: 'Where Is Earth's Water?' (teacher-prepared)
- Optional: Salt, stir sticks (to demonstrate saltwater taste/unsuitability)
- Optional: Magnifying glasses for close observation
- Printed Four-Quadrant Note Sheet (one per student)
- Exit slip slips (half-sheet printed)
- ELL support: bilingual vocabulary cards (water cycle terms in home languages)
Scaffolded Task Progression
Your group has a 1-liter (1,000 mL) graduated cylinder representing ALL of Earth's water.
Step 1: Use the large measuring cup to pour 970 mL of blue (saltwater) into the cylinder. This represents Earth's oceans and seas.
Step 2: Use an eye dropper to carefully add 30 mL of light blue water. This represents ALL of Earth's freshwater.
Step 3: Now, from that 30 mL of freshwater, use the eye dropper to separate out just 3 mL into a small cup. This represents freshwater that is NOT frozen in glaciers or ice caps.
Step 4: From those 3 mL, use the eye dropper to place just 1 drop (~0.3 mL) onto a piece of dark paper. This tiny drop represents ALL of Earth's accessible, drinkable surface and groundwater.
Record in your data table:
| Water Type | Amount (mL) | % of Total |
|---|---|---|
| Saltwater (oceans) | 970 mL | 97% |
| All freshwater | 30 mL | 3% |
| Freshwater NOT frozen | 3 mL | 0.3% |
| Accessible potable water | ~0.3 mL | ~0.03% |
Discussion: What surprises you? Turn and talk to your partner.
*Support option: Use the printed reference card showing the completed table. Match each container to the color on the card.*
Use the anchor chart and the diagram below to answer the questions.
[ Interactive graph / diagram — available in the full lesson ]
Answer these questions using the diagram:
1. What percentage of Earth's water is saltwater?
2. What is the largest source of freshwater on Earth? Can people easily use it? Why or why not?
3. What percentage of freshwater is groundwater? Is groundwater easy to access?
4. What tiny fraction is surface water (rivers, lakes)? Why does this matter for cities?
*Support option: Use the vocabulary card set to match each term before answering.*
*Challenge: Convert the freshwater percentages to 'out of 1,000 mL' using your data from Task 1.*
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