Treatment Stages
Getting started
New to this tool? Turn on Worked example beside the page title to load a coagulation stage with pH control, then chlorination, fluoridation and a final lime trim to pH 7.8. Turning it off brings back whatever you had entered. Clear all at the foot of this tab removes every chemical dose and keeps the stages.
Work through the tabs in order: the treatment stages here, then Water Quality and Corrosivity, and with Premium, Chemical Costs, Solids Load, Design Ranges, Scenarios and Report & Save. The source water panel on the left stays in view on every tab. Chemical strengths and chemistry factors are in Settings; the basis and limitations are in About this model. This tool provides guidance only.
Set your source water quality in the left panel, then build your treatment train as a sequence of stages — typically coagulation first, then any intermediate dosing, then post-filtration conditioning. Within a stage, chemicals are applied in the order listed, and water quality carries forward from one stage to the next.
Each chemical can be dosed in the units you work in (product, active, as-metal, ppm v/v, as-Cl₂, as-F). The running water quality after each stage shows beneath it — switch to the Water Quality and Corrosivity tabs for the full picture. Chlorine residuals are cumulative across dose points, with inorganic demand (NH₃, Fe, Mn from the source water) consumed by the first dose point.
Tip: the CO₂ entry accepts a negative dose to model CO₂ stripping (aeration) — e.g. −10 strips 10 mg/L of free CO₂ and raises pH.
Water Quality
Guide: using this tab
Tracks every water quality parameter from source through each treatment stage, so you can see exactly what each dosing point does to pH, alkalinity, calcium, chloride, sulphate, conductivity and chlorine residual.
Read it left to right as water moves through the plant. Values outside typical guideline ranges are flagged. Use it to sanity-check a treatment train — e.g. confirming final pH and residual land where intended, or spotting unintended chloride/sulphate build-up from coagulant and acid selection.
Corrosivity
Guide: using this tab
LSI — Langelier Saturation Index
The difference between the actual pH and the pH at which the water would be exactly saturated with calcium carbonate (pHs). It indicates the thermodynamic tendency of the water:
| LSI > +0.5 | Strongly scale-forming — CaCO₃ deposition likely |
| 0 to +0.5 | Mildly scale-forming — often a target for corrosion control |
| -0.5 to 0 | Mildly aggressive — slowly dissolves CaCO₃ |
| LSI < -0.5 | Aggressive — undersaturated, corrosive towards cement and CaCO₃-protected surfaces |
LSI tells you the direction of the tendency but not the amount — use CCPP for that.
CCPP — Calcium Carbonate Precipitation Potential
The mass of CaCO₃ (mg/L) the water would precipitate (positive) or dissolve (negative) in reaching equilibrium. Unlike LSI, CCPP is quantitative: water with high alkalinity and calcium can deposit much more scale at the same LSI than a soft, low-alkalinity water. Typical corrosion-control targets are slightly positive values (around +1 to +5 mg/L); large positive values risk scaling of pipes, heaters and membranes; strongly negative values indicate water that will strip cement linings and provide no protective film.
RSI — Ryznar Stability Index
An empirical re-arrangement of the same saturation chemistry (RSI = 2×pHs − pH), developed from observations of scale in steel mains. Interpretation runs opposite to LSI: RSI < 6 suggests scale-forming water, 6–7 approximately balanced, and > 7 increasingly aggressive/corrosive.
AI — Aggressiveness Index
A simplified screening index (pH + log₁₀[alkalinity × calcium hardness]) originally developed for asbestos-cement pipe. AI < 10 is highly aggressive, 10–12 moderately aggressive, > 12 non-aggressive. It omits temperature and ionic strength, so treat it as a coarse screen only.
Larson's Ratio (Larson-Skold Index)
The ratio of aggressive anions (chloride + sulphate, in equivalents) to the buffering capacity (alkalinity, in equivalents). It addresses corrosion of iron and steel rather than CaCO₃ chemistry: chloride and sulphate interfere with the formation of protective scales on ferrous surfaces.
| < 0.8 | Chloride and sulphate unlikely to interfere with natural film formation |
| 0.8 – 1.2 | Some interference; corrosion rates may be elevated |
| > 1.2 | High rates of localised corrosion expected on iron/steel |
Note these indices describe tendencies under equilibrium assumptions — actual corrosion and scaling depend on pipe material, flow, temperature, biofilms and water age. Use them together, not in isolation.
Chemical Costs
Guide: using this tab
Enter delivered chemical prices as $ per tonne of product and the model converts your doses into daily usage and annual spend per chemical and in total.
If your supplier quotes $/m³, multiply by the specific gravity to get $/tonne (the SG for each chemical is shown alongside, and the converter is built into the table). Costs entered here also feed the Scenarios tab so alternative chemicals are compared on a like-for-like annual cost basis.
Solids Load
Guide: using this tab
Estimates the dry solids your plant produces: source turbidity (converted via the NTU→SS factor), removed colour/organics, coagulant hydroxide precipitate (from the Al or Fe dose) and any PAC. This is the load your clarifiers, washwater recovery and residuals handling must deal with.
With Design Ranges enabled, you can extend the analysis to high-solids events: the governing design inputs become the event magnitude, its duration, and the recovery time before the next one — these size the residuals processing capacity and buffer storage.
Design Ranges
Guide: using this tab
Takes your treatment train from a single operating point to a design envelope. Define minimum / average / maximum source water conditions, set coagulant doses for each, and the model auto-calculates the acid, base and chlorine doses needed at each condition: acids/bases target your pH setpoints; chlorine carries the average dose plus the organic demand you enter.
The outputs are dosing-system design parameters — dose ranges, dosing pump flow rates and turndown ratios, and chemical storage sized to your delivery and day-tank arrangements. Work top to bottom: ranges → doses → setpoints → review the requirement tables.
Scenarios
Guide: using this tab
Compares alternative chemicals against what you're currently dosing, on an equivalent-performance basis: coagulants are matched by metal ion content, bases and acids by the alkalinity change needed to reach the same pH, and chlorine sources by Cl₂ equivalents.
Each alternative shows the equivalent dose, daily usage and annual cost versus your current chemical (using prices from the Chemical Costs tab). Use it for procurement comparisons and to test switching — e.g. alum to PACl, or caustic to lime — before running jar tests.
Report & Save
Guide: using this tab
Save / Load Project stores every input you've used (and a snapshot of results) as a JSON file you can reload later — only sections you've actually configured are saved.
Reports: select the sections to include, then export. Print / Save as PDF opens your browser's print dialog with a formatted report — choose "Save as PDF" as the destination. Export CSV downloads the same data as a spreadsheet-ready file.
Reports reflect the current model state — re-export after making changes.