Lab / experiment Grade 3 Science
Build a Rain Gauge and Keep a Rainfall Record
Third graders build a working rain gauge from a bottle, site it outdoors correctly, and keep a month-long class rainfall log they total and graph on a scaled bar graph.
Objectives
- Build a working rain gauge from a bottle, using a funnel, a pebble layer, and a zero line marked in centimeters.
- Site a rain gauge correctly so its readings are fair and accurate.
- Read the gauge and record daily rainfall in a class log for about one month.
- Total a month of readings into weekly amounts and graph them on a scaled bar graph.
Vocabulary
- Precipitation
- Precipitation is any water that falls from clouds to the ground, including rain, snow, sleet, and hail. It is the main way water returns from the sky to the surface of the Earth.
Also: rain gauge, meniscus, ballast, scaled bar graph
Teacher overview
A rain gauge turns something students already notice, whether a day felt rainy or dry, into a number they can log, compare, and graph: how much rain actually fell at our school this month? In this project, students build a working rain gauge from a single plastic bottle, using the same three design ideas found in the simple gauges hydrologists and backyard weather-watchers rely on everywhere: straight sides, a funnel cut from the bottle's own top, and a zero line that accounts for the pebbles holding the gauge steady in wind. Once the gauge is built, tested indoors, and sited correctly outside, the class reads it on school days for about a month, logs each reading, and turns four weekly totals into one scaled bar graph, the same graph skill Grade 3 mathematics introduces this year.
Watch for this misconception: students often assume a wider bottle would show a bigger, more impressive rain number than a narrower one, since a wider opening looks like it should catch more. Point out that as long as a gauge's sides stay straight and vertical, the depth of water it collects always matches the actual depth of rain that fell, no matter how wide or narrow the bottle is; a wider gauge simply spreads the same rain over more area, so the depth reading comes out the same. This is exactly why the straight-sided design matters, and why a curved or tapered container would give a false reading. Question 7 in the analysis section returns to this idea directly, asking students to compare two gauges of different widths.
Procedure
Safety. An adult removes the cap and cuts the bottle in Steps 1 and 2. Students should not use scissors or a knife on the bottle. Wipe up spilled water right away, since a wet floor is slippery. Outside, only check the gauge when it is safe. Wait until a storm fully passes. Watch for wet, muddy ground before you walk out to read it.
Session 1: build the gauge (about 45 min).
Step 1. An adult removes the cap from the bottle and sets it aside. Taking the cap off first opens the neck, so rain can flow through it later.
Step 2. An adult cuts the bottle where the straight sides end and the curved top begins, about a third of the way down from the cap. This cut leaves two pieces. The bottom piece has straight sides. The top piece is shaped like a funnel.
Step 3. Turn the top piece upside down. Slide its open neck down into the bottom piece, so it sits like a funnel. A narrow top lets in less wind. Less water splashes back out. The narrow top also shades the water below, so less of it dries up between readings.
Step 4. Tape around the rim where the funnel meets the straight sides. This keeps the two pieces from sliding apart or tipping.
Step 5. Add about a half cup of small pebbles to the bottom of the bottle. Spread the pebbles out flat. The pebbles act as ballast. Their weight helps keep the finished gauge from tipping over in wind.
Step 6. Slowly pour water in until it just covers the top of the pebble layer, flat across the whole bottom. Mark this water line on the outside of the bottle with a marker, and label it "0." Pebbles take up space at the bottom of the bottle. The zero line sits at the top of the pebbles, not at the true bottom. This zero line makes every later reading correct.
Step 7. Make the ruler scale. Starting at the height of the zero line, use the ruler to mark straight cm lines going up the index card strip. Number them 0, 1, 2, and on up.
Step 8. Slide the marked strip into the plastic sleeve to keep it dry. Tape the sleeve to the outside of the bottle. Line up its "0" mark right at the zero line from Step 6.
Step 9. Test the gauge before it goes outside. Pour a small, measured amount of water in above the zero line. Check that the scale rises by a good amount for that much water. Fix the scale if the numbers look wrong. Then pour the test water back out, down to the zero line.
Session 2: site the gauge and start the log (about 15 min, then about 5 min each school day after).
Step 10. As a class, choose one open, level spot for the gauge. Keep it away from the school building, walls, and trees. A roof edge or a branch can block rain from reaching the gauge, or drip extra water into it. A simple rule: keep the gauge as far from a wall or tree as that wall or tree is tall.
Step 11. Push three stakes into the ground in a small circle around the bottle. Tie or tape the bottle to the stakes. This keeps wind from tipping it over.
Step 12. Check that the gauge stands straight up and down, not leaning. Use a level, or a string with a washer tied to the end. A leaning gauge does not read correctly.
Step 13. Each school day, a student reader reads the water height at eye level. Read it at the bottom of the curved surface where the water meets the air. This curve is called the meniscus. Read to the nearest half cm. Record the date, the reading, and a short weather note on the class log sheet.
Step 14. On the last school day of each week, record that day's reading as the week's total. Then pour the water out. Refill with clean water up to the zero line. The gauge is now ready for the next week.
Step 15. After about four weeks, use the four weekly totals in the next section. Note that a heavy weekend rain will show up as a jump in Monday's reading, since no one reads the gauge on days school is closed.
Data & Analysis
Daily log, one week (repeat for each week of the month).
| Date | Day | Reading (cm) | Weather note | Recorder |
|---|---|---|---|---|
| Monday | ||||
| Tuesday | ||||
| Wednesday | ||||
| Thursday | ||||
| Friday |
Weekly totals.
| Week | Ending reading (cm) = week's total |
|---|---|
| Week 1 | |
| Week 2 | |
| Week 3 | |
| Week 4 | |
| Month total |
Suppose one class's four weekly totals were 2 cm, 5 cm, 1 cm, and 3 cm. Add these four numbers. What is that month's total rainfall?
Using your own class's four weekly totals, find your month's total rainfall. Show your addition.
Which of your class's weeks had the most rain? Which had the least? Find how many more cm fell in the wettest week than in the driest week.
On your scaled bar graph, what amount does each grid line stand for? Explain why the class picked that scale.
Look at the weather notes from the week with the most rain in your log. Name one note that helps explain the high total.
A gauge placed too close to a wall or a tree can give a false reading. Explain, in your own words, why a rain gauge needs open space around it.
Two pairs built gauges from bottles of different widths. Both gauges have straight sides. The pairs set both gauges out in the same rain at the same time. Would their cm readings match, or would they differ? Explain your thinking.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
Answer: 11 cm.
Add 2 + 5 + 1 + 3 to get 11. This item checks the addition itself, separate from the class's own real data in Question 2.Answer: Answers will vary; the total should equal the sum of the class's own four weekly readings, with the addition shown and correct.
Answer: Answers vary based on the class's own data; accept any response that correctly names the highest and lowest week from the actual log and subtracts one from the other to find the difference.
Answer: Answers vary depending on the scale the class chose, such as one grid line standing for 1 cm or for 2 cm. Accept any explanation that connects the chosen scale to keeping the graph a readable size for the range of totals the class collected.
Answer: Answers vary; accept any weather note that logically points to more rain, such as "storm," "heavy rain," or "steady rain," rather than a note like "sunny" or "clear."
Answer: A wall, a roof edge, or a tree branch can block rain from reaching the gauge, or can drip extra water into it after the rain has passed, so the reading no longer matches the rain that actually fell in the open.
A fair reading depends on the gauge sitting in a spot where only direct rain, nothing blocked and nothing added, reaches the opening.Answer: The two readings should match closely, since both gauges have straight sides.
The depth of water a straight-sided gauge collects depends on how deep the rain fell, not on how wide the bottle is; a wider gauge catches more total water, but that water spreads across more area, so the depth comes out the same as in the narrower gauge.
Differentiation
Support (below grade level)
Pre-mark the zero line and the centimeter scale ahead of time so pairs focus on assembling and siting the gauge rather than measuring it from scratch. Reduce the daily log to three readings a week (Monday, Wednesday, Friday) instead of five, and provide the month-total addition in Question 1 already lined up in a vertical column.
Extension (above grade level)
Have advanced pairs build a second gauge with a narrower straight-sided bottle, site it beside the class gauge, and compare the two sets of readings over a week to test the answer they gave to Question 7 with real data instead of reasoning alone. Ask them to write two or three sentences explaining any small difference between the two gauges' readings.
ELL supports
Pre-teach rain gauge, ballast, funnel, and meniscus using the actual gauge as a visual reference, pointing to each part while naming it. Provide the daily log sheet with a small picture key for weather notes (a sun, a cloud, raindrops, a lightning bolt) alongside the words, so students can record conditions with an icon when a written note is still developing.
Extensions
Invite a local water utility or National Weather Service volunteer to describe how their rain gauges compare with the class's bottle version, including how often real gauges are read and what the data is used for. Pairs may also take their own tested gauge home for a week, keep a personal rainfall log, and bring their totals back to compare with the class's siting and results, discussing why two gauges in different yards might show different numbers even on the same rainy day.