Drinking-Water Hardness across Ward Sources: An EDTA Titration Study with Quality Control

What this study does. Hardness — dissolved calcium and magnesium — is the water-quality parameter every household notices first: kettles scale, soap refuses to lather, geysers waste heat. In a Bengaluru ward, three very different waters arrive in one neighbourhood: treated BWSSB piped supply, deep borewell groundwater, and tanker/sump water of mixed origin. IS 10500:2012, the Indian drinking-water standard, sets total hardness at an acceptable limit of 200 mg/L as CaCO₃ and a permissible limit of 600 mg/L in the absence of an alternate source. This project measures, with proper analytical quality control, where the ward actually stands.

An individual student samples 24 points across one ward — 8 piped-supply taps, 8 borewells, 8 tanker/sump-fed points — following a written protocol (pre-rinsed, labelled PET bottles, analysis within 24 hours). Total hardness is titrated with standardised EDTA at pH 10 (ammonia buffer, Eriochrome Black-T indicator) following APHA Standard Methods 2340 C; calcium hardness is titrated separately with murexide at pH 12–13, giving magnesium by difference; pH and TDS are logged at source.

The analytical honesty is the point of the study: EDTA is standardised against standard CaCO₃ before every batch, a reagent blank and a duplicate in every five (relative percent difference target ≤ 5 %) run with it, and one spike-recovery check validates the method on the ward's own matrix. Results are compared by source type with a Welch t-test and every value is judged against IS 10500:2012 — a small, defensible water-quality assessment, not a heap of titration readings.

Households in a mixed-supply ward receive water whose hardness depends on which source filled their tank — piped treated supply, a borewell, or a tanker-fed sump — but nobody in the ward knows the actual numbers. Hardness is not the most dangerous parameter, but it drives real decisions: filter and softener purchases, geyser descaling, and the belief that 'borewell water is bad water', which may or may not be true for this particular ward.

At the student level, hardness titration is taught as an isolated practical; the assessment skills that make it an analysis — standardisation, blanks, duplicates, spike recovery, chain of custody, standard-based reporting — are usually skipped. Quoting uncalibrated titration values against an unspecified basis produces numbers that cannot be defended, let alone acted on.

This project therefore measures total and calcium hardness at 24 ward sources with a full analytical quality-control frame, compares the three source types statistically, places every result against IS 10500:2012, and delivers a ward-level hardness assessment with its uncertainty stated — demonstrating that an undergraduate can produce genuinely defensible water-quality data.

Abstract

This single-member analytical study covers drinking-water hardness across one Bengaluru ward. Twenty-four points — eight BWSSB taps, eight borewells, eight tanker/sump-fed points — are sampled under a written protocol and analysed for total hardness (EDTA, APHA 2340 C), calcium hardness (murexide) and magnesium by difference, with pH and TDS logged at source. EDTA is standardised against calcium carbonate each batch; blanks, duplicates (RPD ≤ 5 % target) and a spike recovery provide the QC frame. Results are compared by source type with a Welch t-test, mapped across the ward, and assessed against IS 10500:2012.

Introduction

Bengaluru's water is mixed: BWSSB supplies treated Cauvery water to connected households, borewells tap the hard-rock aquifer beneath the city, and tankers fill sumps where the network falls short. They differ in hardness because their histories differ — surface water is softened by treatment, deep groundwater dissolves calcium and magnesium from rock over decades. Households experience it as scale, and IS 10500:2012 sets numbers: 200 mg/L as CaCO₃ acceptable, 600 mg/L permissible in the absence of an alternate source.

Existing knowledge and the gap

The method is classical — APHA 2340 C and Vogel's quantitative-analysis texts give the complexometric theory with Eriochrome Black-T and murexide indicators. What student projects omit is everything that makes the numbers trustworthy: EDTA standardisation against a primary standard, blanks, duplicates with a stated precision target, spike recovery, a chain of custody from tap to burette; they also quote hardness without the 'as CaCO₃' basis or compare against no standard. The gap this project fills is a complete, QC-framed ward-scale assessment: a designed sampling grid, documented procedure, uncertainty-aware reporting and a regulatory verdict per source.

Proposed study

1. Map the ward (fictional name) into three source types and select eight points per type with resident permission.
2. Prepare and standardise 0.01 M EDTA against CaCO₃; prepare ammonia buffer, EBT, murexide and NaOH.
3. Sample all 24 points in two rounds (12 points per day) in pre-rinsed labelled bottles, with pH and TDS logged at source.
4. Titrate total hardness (pH 10 buffer, EBT) and calcium hardness (murexide, pH 12–13) within 24 hours; magnesium by difference.
5. Run the QC frame per batch: blank, duplicate every fifth sample (RPD ≤ 5 %), one spike recovery across the study.
6. Analyse: mean ± SD per source type, Welch t-test borewell vs piped, per-point IS 10500 classification, ward map of results.

Feasibility

• Technical: the titration needs standard glassware, a balance, pH/TDS meters and reagents — all B.Sc chemistry lab stock; APHA's metal-ion interferences are handled with standard buffer additions.
• Economic: reagents and bottles cost under ₹600; transport within the ward is the only other cost.
• Operational: an individual student can finish in 12 weeks at 8 h/week — the 24-hour analysis window is the binding constraint, so sampling and titration days are paired in advance. Private borewells need recorded consent. Endpoint subjectivity and short holding times are the main risks, addressed by QC.

In scope

• One ward (fictional name), 24 points in three source types, two sampling rounds, analysed for total hardness, calcium hardness, magnesium by difference, pH and TDS.
• Full QC frame: EDTA standardisation, blanks, duplicates (RPD), one spike recovery.
• Statistical comparison by source type and IS 10500:2012 classification of every point.

Out of scope

• Other parameters (chloride, nitrate, fluoride, coliforms) — each needs its own method and some need a partner lab; listed under future scope.
• Trace metals by instrument (AAS/ICP) — beyond an undergraduate titration lab.
• Water-treatment or softening trials (boiling, ion exchange) — a separate experimental project.
• Temporal trend analysis beyond the two rounds; seasonal monsoon effects are noted as a limitation.

Research design: an observational analytical study with a stratified sampling design (source type as stratum) and a pre-planned analytical quality-control frame. Reporting follows APHA 2340 C conventions with all hardness values expressed as mg/L as CaCO₃.

Sampling design (Weeks 1–2): the ward (fictional name, Bengaluru) is mapped into the three source types; eight points per type are selected spread across the ward's localities, with the resident or caretaker's consent noted per point. Points are coded W-01 … W-24 (W-type-number) and their coordinates logged on the sample map. Sample bottles: clean PET, pre-rinsed three times at source, filled to the neck, labelled with point code, date and time.

Reagents and standardisation (Week 3, repeated per batch): 0.01 M EDTA prepared from disodium EDTA and standardised by titrating aliquots of standard calcium carbonate solution (primary standard, dried and weighed); the standardisation is repeated each sampling batch and the factor recorded. Ammonia buffer pH 10 with inhibitor, EBT indicator, murexide indicator, 4 N NaOH for the calcium step.

Titration procedure (Weeks 4–9, paired sampling-titration days): total hardness — 25 mL or 50 mL aliquot, 2–3 mL buffer to pH 10 ± 0.1, 2–3 drops EBT, titrate wine-red to pure blue; calcium hardness — aliquot, NaOH to pH 12–13 (magnesium precipitated as hydroxide), murexide, titrate pink to purple; duplicate aliquots per sample and the duplicate-sample QC as planned. pH and TDS measured at source with calibrated meters (pH meter calibrated with 4/7 buffers that morning).

Quality control: one reagent blank per batch (should read zero drops); a duplicate in every five samples with relative percent difference target ≤ 5 %; one spike-recovery check (a sample fortified with a known CaCO₃ aliquot; target recovery 95–105 %); endpoint colour between analysts is n/a here, so a photograph of each endpoint colour is archived to make the endpoint judgement auditable.

Analysis plan (Weeks 10–11): compute hardness as (V_EDTA × M_EDTA × 100,000) / V_sample mg/L as CaCO₃ (with standardisation factor); tabulate mean ± SD per source type; Welch t-test (borewell vs piped) because sample sizes and variances may differ; box plots by source type; scatter of hardness vs TDS; per-point classification against IS 10500:2012 (≤ 200 acceptable; 201–600 permissible in absence of alternate source; > 600 non-potable); ward map with values. All computations duplicated once by hand or in Excel as a cross-check.

Timeline (12 weeks): Weeks 1–2 ward mapping, permissions, method practice; Week 3 reagents and standardisation; Weeks 4–9 paired sampling-titration days (12 points per fortnight); Week 10 spike recovery and re-runs; Weeks 10–11 analysis; Week 12 report, slides and viva.

The study is a field-to-burette-to-verdict pipeline with a quality-control gate at each stage. Every result is traceable from the tap to the standardisation factor behind its titre.

flowchart TD
  A["Map ward: 8 piped + 8 borewell + 8 tanker/sump points"] --> B["Resident consent recorded per point"]
  B --> C["Sample in pre-rinsed labelled bottles; log pH and TDS at source"]
  C --> D["Analyse within 24 h"]
  D --> E["Standardise 0.01 M EDTA vs standard CaCO3"]
  E --> F{"QC gate: blank zero, duplicate RPD <= 5 pct?"}
  F -->|Pass| G["Total hardness: EBT at pH 10"]
  F -->|Fail| H["Investigate, restandardise, repeat batch"]
  G --> I["Calcium hardness: murexide at pH 12-13; Mg by difference"]
  I --> J["Spike-recovery check (95-105 pct target)"]
  J --> K["Statistics: source-type means, Welch t-test, hardness vs TDS"]
  K --> L["IS 10500:2012 classification per point"]
  L --> M["Ward map and assessment report"]

Data organisation

One row per sample per parameter with point code, source type, date, time, aliquot volume, titre volumes (all replicates, not just the mean), the EDTA standardisation factor of that batch, and the computed value. The computation from titres to mg/L as CaCO₃ is scripted once, so a corrected titre propagates cleanly; the hand-calculation of two representative samples is shown in the report appendix.

Core calculation (abridged)

Hardness (mg/L as CaCO3) = (V_edta × M_edta × 100000) / V_sample
  V_edta: mean titre (mL) of the two replicates
  M_edta: molarity after CaCO3 standardisation
  V_sample: aliquot volume (mL)
RPD (duplicates) = |A - B| / ((A + B)/2) × 100 %
Spike recovery % = (found - native) / added × 100

Results tables to fill (no numbers are pre-filled)

• Full potability panel: chloride (argentometry), fluoride (SPADNS), nitrate and coliforms (partner lab) to complete the IS 10500 picture for the ward.
• Seasonal rounds: pre- and post-monsoon sampling to quantify how recharge changes borewell hardness.
• Depth dimension: hardness versus borewell depth, if owners share drilling records.
• Softening trials: boiling and zeolite/ion-exchange mini-trials on the two hardest sources, measured with the same method.
• Instrument upgrade: comparison of the titration with an AAS measurement of calcium and magnesium at a partner institution.
• A repeatable ward water-quality booklet handed to the ward office and residents' association.