Water tankers needed daily in a metro summer
A gap analysis — estimate demand, estimate supply, size the shortfall.
Estimate the number of private water-tanker trips per day in a 10-million metro at summer peak. This is a gap guesstimate: tankers don't serve total demand — they serve the shortfall between municipal supply and need. Size both sides, then convert the gap to trips.
Demand
Norm ~135 litres/person/day × 10M × 1.15 summer factor + ~20% commercial/institutional ≈ 1,850 MLD (million litres/day).
Effective supply
Installed municipal ~1,500 MLD, minus summer reservoir dip (~10%) and distribution losses (~25%) → ~1,200 MLD reaching users.
The gap
~650 MLD. Private borewells and storage absorb ~60%; tankers serve the rest ≈ 260 MLD.
Trips
Standard tanker = 10,000 L → 260 MLD ÷ 10K ≈ 26,000 trips/day, by roughly 6–7K tankers doing ~4 trips each.
How to defend it
Structure-first wins here: announcing "tankers serve the demand-supply gap, so I'll size both sides" is 80% of the marks before any arithmetic. The leakage assumption (~25%) is India-realistic and worth citing — it's often the biggest single term in urban water math.