Water quality testing helps students compare how clean and safe different water sources are using evidence instead of guesses. In this project, tap water, pond water, and stream water are tested for pH, hardness, nitrates, and chlorine with water quality test strips. These measurements matter because water chemistry affects drinking safety, aquatic life, and local ecosystems.
A well-designed test also teaches how scientists control variables and organize data.
Key Facts
- pH measures acidity or basicity on a scale from 0 to 14, with 7 being neutral.
- A change of 1 pH unit means a 10 times change in hydrogen ion concentration.
- Concentration is often measured in parts per million, written as ppm, where 1 ppm = 1 mg/L in water.
- Average value = sum of measurements / number of measurements.
- Range = highest value - lowest value.
- Good comparisons require testing each sample the same way, at the same time, and with the same type of strip.
Vocabulary
- pH
- A measure of how acidic or basic a water sample is.
- Hardness
- The amount of dissolved calcium and magnesium minerals in water.
- Nitrate
- A nitrogen compound that can enter water from fertilizer, animal waste, and runoff.
- Chlorine
- A chemical often added to treated tap water to kill harmful microorganisms.
- Variable
- A factor in an experiment that can change, such as water source, location, season, or testing time.
Common Mistakes to Avoid
- Touching the test pads with fingers before testing, which can contaminate the strip and change the color result.
- Reading the strip too early or too late, which is wrong because the color reaction must be compared at the time listed in the strip instructions.
- Using different containers for different sources without rinsing them, which can leave residue that affects pH, chlorine, or nitrate readings.
- Comparing only one test from each source, which is weak evidence because repeated trials help reveal random error and improve reliability.
Practice Questions
- 1 A student measures nitrate in pond water three times and gets 8 ppm, 10 ppm, and 12 ppm. What is the average nitrate concentration?
- 2 Tap water has pH 7.5, pond water has pH 6.5, and stream water has pH 7.0. What is the pH range for these three samples?
- 3 A stream sample tested after heavy rain has higher nitrate than the same stream tested during a dry week. Explain one likely reason and identify the variable that changed.