Effect of Domestic Hot Water pH on Plumbing Metal Leaching

Problem Statement

This experiment determines whether changing the pH of household hot water, within realistic domestic ranges, alters the amount of metal leached from typical plumbing materials during a single day of exposure. No regulatory, safety, or health conclusions are drawn.

Hidden Assumption Being Tested

Modest pH variation in domestic hot water does not meaningfully affect metal leaching from plumbing materials over short time scales.

What Might Be True Instead

Even small, realistic changes in hot water pH may significantly increase metal leaching from common plumbing materials.

Materials and Preparation

  • Copper pipe coupons (2 cm × 5 cm, cleaned, uncoated)
  • Galvanized steel pipe coupons (2 cm × 5 cm, cleaned, uncoated)
  • Deionized water
  • Dilute HCl and dilute NaOH for pH adjustment
  • Calibrated pH meter
  • Hot water bath or temperature-controlled incubator
  • Polyethylene bottles with tight-sealing lids
  • ICP-MS or equivalent trace metal analyzer
  • Clean pipettes and sample vials
  • Personal protective equipment

Experimental Parameters

  • pH values: 6.5, 7.5, 8.5
  • Neutral control: unadjusted water (≈ pH 7.0)
  • Temperature: 60 °C (±2 °C)
  • Exposure time: 24 hours

Experimental Procedure

  1. Adjust deionized water to target pH values using dilute HCl or NaOH.
  2. Place one copper coupon and one galvanized steel coupon into separate bottles for each pH condition.
  3. Add 100 mL of prepared water to fully submerge each coupon.
  4. Seal bottles and place in a 60 °C water bath or incubator for 24 hours.
  5. After exposure, allow bottles to cool to room temperature.
  6. Remove coupons with clean forceps and gently mix the water.
  7. Collect 50 mL of each water sample into labeled vials.
  8. Measure and record final pH of each sample.

Analytical Method

  • Calibrate ICP-MS using standards for copper, lead, zinc, and iron
  • Analyze samples for metal concentrations (µg/L)
  • Run procedural blanks to verify background levels

Binary Exceedance Condition

For each metal and material, calculate the difference between the test pH condition and the neutral control.

  • TRUE: Any pH condition yields a concentration ≥10 µg/L higher than the neutral control.
  • FALSE: No pH condition exceeds the neutral control by ≥10 µg/L.

Controls and Confounders

  • Coupons must be fully uncoated and thoroughly rinsed
  • pH drift greater than ±0.3 invalidates the run
  • Temperature must remain within ±2 °C
  • Cross-contamination between samples must be avoided
  • Each condition performed at least in duplicate

Output

Report measured metal concentrations and note any exceedance events. The outcome is strictly binary per metal and material.

Scope Boundaries

This experiment does not assess health risk, regulatory compliance, water safety, or engineering recommendations. Results apply only to the defined materials, pH range, and exposure conditions.

Edge-of-Practice experiments are designed for short-cycle execution, clear falsification, and direct reproducibility. No extrapolation is permitted.