Calculator
Editable inputs
| Stream | Type | Flow m³/h | Remove |
|---|---|---|---|
Calculated outputs
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About this tool
Close the water balance for the whole site before sizing end-of-pipe treatment. Mark each stream as an input, output, internal recycle or storage change on one time basis, and the tool reports any unaccounted water and draws the flows as a Sankey diagram.
Internal recycle stays separate, so it is never counted as new water.
Method and equations
Σ external inputs = Σ external outputs + increase in storageE = Σ inputs − Σ outputs − ΔS|E| / Σ external inputsrecycle / (Σ external inputs + recycle)Assumptions
- All streams share one physical boundary and one time basis (m³/h here; daily or annual averages also work if used consistently).
- Storage change is positive when site inventory increases and negative when it is drawn down.
- Internal recycle is reported separately and is not counted as new external water.
- Evaporation, product incorporation and other losses are external outputs.
Limitations
- Internal recycle improves water efficiency but is never new external water. Counting it as an input inflates supply and hides the real closure error.
- The balance is only as good as the metering behind it. Estimated streams should be flagged and confirmed.
- It closes water volumes only. Salt and constituent loads need the mass balance calculator.
Worked example
A site draws 100 m³/h of municipal water and 50 m³/h from a borehole. Water leaves as 80 m³/h of wastewater discharge, 35 m³/h of evaporation, 25 m³/h of brine sent off site and 5 m³/h incorporated into product. Storage rises by 5 m³/h, and 30 m³/h of recovered water is recycled internally.
- External inputs: 100 + 50 = 150 m³/h.
- External outputs: 80 + 35 + 25 + 5 = 145 m³/h, plus 5 m³/h into storage.
- Closure error: 150 − 145 − 5 = 0 m³/h. The balance closes.
- Internal recycle ratio: 30 / (150 + 30) = 16.7%.
If the 30 m³/h recycle had been entered as an external input, inputs would read 180 m³/h and the balance would show a false 30 m³/h gap. That is the most common mistake this tool is built to prevent.
The calculator above opens with these default values. Use Reset to defaults to return to them.
Frequently asked questions
Why is internal recycle not counted as an input?
Recycled water has already entered the site once. Counting it again would double count the same water and make supply look larger than it is.
What sign should storage change have?
Positive when tanks, ponds or other inventory increase over the period, negative when inventory is drawn down. A drawdown appears on the input side of the Sankey.
How close should my balance be?
It depends on metering quality. A gap of a few percent is common on real sites; a large gap usually points to an unmetered stream, an evaporation estimate or a time-basis mismatch.
Can I use daily or annual figures?
Yes, as long as every stream uses the same basis. The tool labels flows in m³/h, but the arithmetic is the same for m³/d or m³/year.
Related ZLD guide chapters
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Brine Consulting screening tool. Results are not a design guarantee, vendor guarantee, regulatory determination or detailed process design, and do not replace project-specific modelling, pilot testing or professional engineering review.