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Office air & water audit calculator
For facilities and admin teams building an approval note: headcount, area, zones and feed TDS in — plant capacity, purifier count, indicative capex, annual operating cost and cost per employee out, with every assumption stated.
Office air & water audit
Indicative capex
₹1,61,000–₹3,58,000
Annual operating cost
₹40,330–₹83,330
Per employee per year
₹1,813–₹3,873
Water
| Line | Amount | Basis |
|---|---|---|
| Daily requirement | ₹120 | 40 × 3 L — figure shown in litres, not rupees |
| Plant capacity to specify | ₹20 | LPH, sized to produce the day's need in ~60% of the working day |
| Capex (low end) | ₹35,000 | to ₹70,000 depending on pre-treatment |
| AMC per year (low end) | ₹2,800 | to ₹9,800 — 8–14% of capex |
| Electricity per year | ₹2,430 | at ₹9/kWh |
| Year 1, low end | ₹40,230 |
At 450 ppm feed, expect recovery around 55% — roughly 98 litres of reject a day, or 25 m³ a year. Budget for where that goes.
Air
| Line | Amount | Basis |
|---|---|---|
| Treated volume | ₹850 | m³ — figure shown in cubic metres, not rupees |
| Total CADR required | ₹3,400 | m³/h at 4 air changes per hour |
| Units to deploy | ₹9 | ~850 m³/h each, one per closed zone minimum |
| Capex (low end) | ₹1,26,000 | to ₹2,88,000 |
| Filters per year (low end) | ₹27,000 | to ₹63,000 |
| Electricity per year | ₹8,100 | at ₹9/kWh |
| Year 1, low end | ₹1,61,100 |
Unit count is driven by the number of closed zones rather than total area — air does not move between rooms with the doors shut, so one large unit cannot serve four cabins.
This is a budgeting model, not a quotation.
Commercial water treatment is specified against a laboratory water analysis, and any vendor quoting a firm price without one is guessing. Feed TDS alone moves the water capex band by more than 60%, and pre-treatment for iron or hardness is not included above at all. Use these figures for an approval note, then get the water tested.
Office air and water purchases usually go wrong in one of two ways. Water systems are specified on headcount alone, without a feed water analysis, and the plant either runs constantly at its limit or the membranes die early on water they were never designed for. Air purifiers are bought by total floor area, which produces two large units for an office of eight closed cabins, seven of which are unaffected.
Both errors come from the same place: sizing against the wrong variable. For water the binding constraint is feed quality and duty cycle, not headcount. For air it is the number of enclosed volumes, because air does not migrate between rooms with the doors shut, and a CADR figure describes what a machine does to the room it is standing in.
The calculator above sizes against the right variables and shows every assumption, so an engineering or facilities team can substitute their own figures rather than accept ours. What it deliberately does not do is produce a quotation — pre-treatment for iron, hardness or turbidity is not included, and that is precisely the line item that a water analysis exists to determine.
What to attach to the approval note
- A laboratory water analysis. Without it every capex figure in any quotation is a guess, and the difference between guesses is larger than most procurement teams expect.
- The five-year cost, not the capex. Power, consumables, AMC and reject water typically exceed the purchase price over five years, and a decision made on capex alone is being made on the smaller number.
- An itemised AMC inclusion list.“Comprehensive” means different things to different vendors, and the membrane is the item most often excluded.
- The reject water volume and where it goes. On a large plant this is a real utilities and drainage question, and it is easier to design for than to retrofit.
- Zone-by-zone air unit placement. A single total CADR figure with no placement plan is how offices end up with clean meeting rooms and unaffected workstations.
Methodology & assumptions
- Water demand is headcount × litres per person per day, defaulting to 3 litres for an air-conditioned office including tea and coffee.
- Plant capacity is daily demand divided by 60% of the working day, so the plant is not sized to run flat out — then rounded up to a shoppable LPH figure.
- Recovery ratio is banded by feed TDS: about 65% below 400 ppm, 55% to 800, 45% to 1,500 and 35% above. Feed and reject volumes follow from it.
- Water capex is banded per LPH, with the spread reflecting the pre-treatment a given feed water requires. AMC is modelled at 8 to 14% of capex per year, which is the usual commercial range.
- Air volume is floor area × ceiling height, converted to cubic metres, and total CADR is set at four air changes per hour.
- Unit count is the greater of the number of enclosed zones and total CADR divided by a practical per-unit maximum, because CADR does not distribute itself between closed rooms.
- Electricity is applied at the tariff entered, using planning figures of roughly 0.9 kW per 100 LPH for small commercial RO and about 40 W average per air purifier.
- Nothing here includes pre-treatment for iron, hardness or turbidity, plumbing modifications, or civil work. Those are specified against a water analysis and can be a substantial addition.
Indicative planning figures for budgeting only, last reviewed 2026-08-08. Not a quotation and not an engineering specification. Pre-treatment, plumbing modification and civil work are excluded and can be substantial.