Engineering Tool · Water Treatment

Water Stability & Carbonate Chemistry

Calculate carbonate-only speciation and transparent pHs, LSI, and RSI screening values.

Municipal Drinking WaterStage 06 — Distribution & Final Quality

Status: Available

PROJECT · OPTIONAL

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01 · USER INPUT

Design basis and inputs

Measured pH *pH · current water sampleWater temperature *deg C · entered temperature is used in the LSI equation; carbonate speciation uses fixed 25 deg C reference constantsAlkalinity *mg/L as CaCO3 · current water; positive input required for LSICalcium hardness *mg/L as CaCO3 · current water; positive input required for LSITotal dissolved solids *mg/L · current water; positive input required for LSICompare an adjusted-water scenario *option · scenario is user-entered; no chemical dose is calculated

Engineering calculations run locally in this browser after assets load.

02 · CALCULATED RESULT

Results at a glance

Load or enter inputs, then calculate to create an authoritative result.

03 · REPORTING

Exports and verification

CSV contains input and output detail. PDF uses the current calculation and report metadata.

Verification suite

Calculation revision ad185526

69 focused fixtures: LSI/pHs/RSI reference case, carbonate alpha fractions and DIC, active scenario inputs, symmetric diagnostics, 25 deg C speciation basis, structured comparison, exports, and stale-result behavior. Tests are deterministic and run without network access.

Engineering Basis

Methodology

Calculates empirical pHs, LSI, and RSI from entered water properties and uses a carbonate-only speciation approximation with fixed reference constants near 25 °C. These are screening indices, not full geochemical equilibrium, a corrosion rate, or an automatic chemical-dose recommendation.

The empirical saturation-pH calculation uses entered water temperature: A = (log10(TDS) - 1)/10, B = -13.12 log10(T + 273) + 34.55, C = log10(calcium hardness) - 0.4, D = log10(alkalinity), and pHs = (9.3 + A + B) - (C + D).

LSI = measured pH - pHs. RSI = 2 pHs - measured pH.

The carbonate-only V1 approximation uses fixed reference constants at approximately 25 deg C: pKa1 = 6.35, pKa2 = 10.33, and Kw = 1e-14. Alpha fractions are calculated from hydrogen concentration and these constants.

Approximate DIC = (alkalinity equivalents - hydroxide + hydrogen)/(alpha1 + 2 alpha2), with alkalinity converted from mg/L as CaCO3 to equivalents per litre.

For current water and an enabled adjusted scenario, LSI uses the respective entered water temperature. Carbonate-only speciation continues to use fixed 25 deg C constants.

Scenario values are entered directly. The tool does not calculate a chemical dose or predict the effect of a treatment process.

Scope / Limitations

Carbonate speciation uses fixed 25 °C reference constants while empirical LSI uses entered temperature. Outputs are screening indices, not corrosion or scaling guarantees.
LSI and RSI are empirical numerical screening indices; this tool does not assign categorical water-quality status.
Carbonate speciation is a carbonate-only approximation. It omits phosphate, silicate, organic alkalinity, and full geochemical equilibrium.
No corrosion rate, lead or copper compliance, CCPP, chemical-dose solver, or automatic treatment recommendation is provided.
CCPP is deferred.

Engineering Path

Upstream Context

Chlorine / Chloramine CT & Residual Designer Use declared treatment, storage, and finished-water chemistry as context for distribution-quality review.
UV Disinfection Designer Use declared treatment, storage, and finished-water chemistry as context for distribution-quality review.
Clearwell & Storage Turnover Designer Use declared treatment, storage, and finished-water chemistry as context for distribution-quality review.

Current Tool Decision

Water Stability & Carbonate Chemistry Calculate carbonate-only speciation and transparent pHs, LSI, and RSI screening values.

Downstream Engineering Step

Distribution and final-quality review Carry the finished-water basis into utility monitoring, distribution, and project-specific operating review.