Testing Our Water: pH, Hardness & Clarity
Solutions chemistry, applied to Detroit's drinking water and the Great Lakes system.
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Standards
HS-PS1-3 — Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
Why Does This Matter?
Detroit's drinking water comes from the Detroit River and the Great Lakes — roughly 20% of the world's surface freshwater. Municipal treatment plants constantly test and adjust water chemistry (pH, hardness, disinfectant levels) before water reaches homes. This lab uses the same basic tests treatment plants rely on.
Objective
Test pH, hardness, and clarity of tap water and at least one comparison sample, then evaluate results against EPA secondary drinking water guidelines.
Materials
- pH test strips or universal indicator solution
- Water hardness test strips (or soap-shake turbidity method)
- Clear sample cups (at least 2 per group)
- Tap water sample
- Comparison sample (bottled water, filtered water, or a natural water source sample)
- Flashlight (for turbidity observation)
- Safety goggles, gloves
Safety: Do not drink any test samples once indicator chemicals have been added. Wear goggles. Wash hands after handling samples.
Procedure
- Label two sample cups: "Tap Water" and your comparison sample name.
- Fill each cup about halfway with its sample.
- Dip a pH strip into each sample and compare the color change to the reference chart. Record the pH.
- Dip a hardness strip into each sample (or complete the soap-shake test) and record hardness in your data table.
- Shine a flashlight through each sample against a dark background and rate clarity on a 1–5 scale (1 = cloudy, 5 = perfectly clear).
- Compare your results to the EPA's secondary (aesthetic) drinking water standards provided by your teacher.
Data Table
| Sample | pH | Hardness (ppm/grains) | Clarity (1–5) | Within EPA guideline range? |
|---|---|---|---|---|
| Tap water | ||||
| Comparison sample |
Analysis Questions
- Was your tap water sample within the EPA's typical guideline range for pH? What might happen to pipes if pH is too low (acidic) for a long period?
- What does "hardness" measure chemically, and where do those minerals most likely come from?
- Why might a water treatment plant need to test water at multiple points in the system, not just at the source?
- Water leaving a treatment plant can still change chemically before reaching a tap. What role do pipe materials and pH play in that (consider what happened in Flint, MI)?