Reconciled 2026-08-13 against the portfolio financial model’s re-base: this worksheet’s program series, contracted floors, and cost rows are unchanged by it. The re-base adjusted SPV sell-through pricing and financing mechanics, which this worksheet does not use.
School ultrafiltration delivered by LifeStraw; Virridy is the carbon developer. This worksheet counts only Virridy's outlays, and says so everywhere.
The partner funds the filters; the carbon layer finances replacement cycles and turns delivery into credits. That makes this a different model from the Amazi Meza Rwanda worksheet: no full-delivery-cost figure exists here, so no GiveWell-comparable $/DALY is claimed. The honest headlines are climate cost-effectiveness and carbon financing per student-year.
Program: LifeStraw Max gravity ultrafiltration (no power, ~100,000 L per unit) in Kenyan schools; target 4,500 schools and 2M+ students over 20 years. Yield in use 0.020 credits per person-year, adopted 20 August 2026 from the independent due diligence reconstruction (the annex previously carried 0.049), CORSIA channel with 42,000 credits contracted for 2026–2029. A real risk is stated up front: credits are currently held unsold pending CORSIA labeling, and scenario S2 prices that risk.
| Series | 2025 | 2026 | 2027 | 2028 | 2029 | 2030 | 2031 | 2032 | 2033 | Total |
|---|---|---|---|---|---|---|---|---|---|---|
| Net credits (tCO₂e) | 0 | 5,578 | 2,834 | 6,121 | 7,607 | 9,094 | 9,094 | 9,094 | 9,094 | 58,516 |
| Implied students served | 0 | 233,653 | 118,714 | 256,367 | 318,633 | 380,898 | 443,163 | 443,163 | 443,163 | 2,637,755 student-yrs |
| Buy price to partner ($/cr) | 9.20 | 9.20 | 9.30 | 9.50 | 9.60 | 9.70 | 9.80 | 9.90 | 9.90 | — |
| Initial purchases ($) | 210,000 | 808,000 | 242,000 | 0 | 0 | 0 | 0 | 0 | 0 | 1,260,000 |
| Ongoing credit purchases ($) | 0 | 0 | 0 | 119,339 | 149,885 | 181,041 | 212,807 | 214,978 | 214,978 | 1,093,029 |
| Virridy carbon outlays ($) | 210,000 | 808,000 | 242,000 | 119,339 | 149,885 | 181,041 | 212,807 | 214,978 | 214,978 | 2,353,029 |
Updated 24 September 2026: the crediting basis on this page is the yield in use in the portfolio model, adopted 20 August 2026 from the independent due diligence reconstruction under Gold Standard SDWS V2.0. It replaces the yield this worksheet carried in August, and the credit series, cost per tonne and integrity-adjusted cost per tonne are recomputed on it.
Credits and prices are proforma inputs; the implied-students row is a formula (credits ÷ the 0.020 yield in use) and is flagged: the 2026 credit figure includes an issuance backlog, so that year's implied students overstate actual reach. Initial purchases are the guaranteed first batch plus early replacement-cycle financing; ongoing purchases are credits × the contracted buy price from 2028.
| TOTAL VIRRIDY OUTLAYS, 2025–2033 | $2,353,029 | Formula initial purchases + ongoing credit purchases |
| Implied student-years served | 2,637,755 | Formula total credits ÷ 0.049 |
| Carbon financing per student-year | $0.892 | Formula outlays ÷ student-years |
Every figure on this page divides by this one cost, and the build fails programmatically if any figure uses a different denominator. What this cost is NOT: it is not the cost of delivering safe water to these schools. Filters, distribution, and program operations are funded by the partner and do not appear in the proforma. A full-delivery-cost $/DALY would require the partner's capex data and is deliberately not computed.
| Input | Value | Provenance | Basis |
|---|---|---|---|
| Diarrheal incidence, school-age | 0.60 episodes/child-yr | Judgment · flagged | Cloned from the Rwanda model; Kenya-specific GBD lookup pending. Tested 0.30–1.20 in S3–S4. |
| Diarrhea reduction, point-of-use filtration | 34% | Evidence-anchored | Wolf et al. 2022 (Lancet), filtration risk ratio 0.66. |
| School share of daily drinking water | 30% | Judgment · flagged | No time-use survey; same assumption as the Rwanda model. |
| Delivery effectiveness (safe at the point) | 90% | Sensor-measured | Portfolio monitoring record: 90.3% of samples safe under monitored delivery (n=1,685). |
| YLD per episode | 0.002215 DALY | Formula | 0.188 disability weight × 4.3 days ÷ 365 |
| Step | Value | Computation |
|---|---|---|
| Episodes averted, 2025–2033 | 145,288 | 2,637,755 student-yrs × 0.60 × 0.34 × 0.30 × 0.90 |
| DALYs averted (raw) | 322 | episodes × 0.002215. Years lived with disability only; mortality excluded (conservative). |
| $ / DALY, carbon-financing basis | withdrawn see note | The chain behind this figure was built from the Rwanda model and carries no Kenya-specific burden or incidence inputs, so it is withdrawn until those are substituted. Dollars through the carbon layer per DALY in the system, NOT DALYs purchased by Virridy: the partner delivers the health impact. |
| Evidence adjustment (section E) | × 0.432 | 322 → 139 DALYs adjusted |
| $ / DALY adjusted, financing basis | $16,927 | $2,353,029 ÷ 139 |
| xCash, three frameworks | 0.094× / 0.041× / 0.147× | GiveWell default / egalitarian / wellbeing weights; moral-uncertainty weighted 0.097×. Stable, and immaterial: the basis label, not the framework, drives interpretation. |
| Factor | Score | Basis |
|---|---|---|
| Internal validity | 0.80 | Meta-analytic anchor, judgment links in the chain. |
| External validity | 0.75 | Household point-of-use trials transferred to Kenyan school delivery: a cross-country, cross-setting transfer. |
| Publication bias | 0.80 | Systematic review without an independent funnel-plot confirmation here. |
| Implementation quality | 0.90 | Operational program, credits issued and held; CORSIA labeling still pending. |
| Composite | 0.432 | Formula product of the four, reported alongside raw, never silently multiplied in. |
| Residual baseline-practice factor | 0.80 | Judgment · flagged The yield is already reconstructed to SDWS V2.0 (0.049, like Rwanda); this prices residual baseline risk pending a measured school baseline survey. |
| Delivery effectiveness | 0.90 | Sensor-measured The same cell the health chain uses. One usage number, two consumers. |
| Credit integrity ratio | 0.72 | Formula 0.80 × 0.90 × 1.00 leakage |
| $ / tonne, credited basis | $40.21 | $2,353,029 ÷ 58,516 t · 4.6× below the $185 social cost of carbon |
| $ / tonne, integrity-adjusted | $55.85 | $2,353,029 ÷ (58,516 × 0.72) · 3.3× below the SCC |
| CORSIA labeling status | PENDING | Credits are held unsold until labeled. This is the model's load-bearing commercial assumption, priced in S2. |
| Scenario | Varied input | DALYs | $ / DALY fin. basis | $ / tonne | vs SCC | Reading |
|---|---|---|---|---|---|---|
| Base case | — | 322 | withdrawn | $40.21 | 4.6× | as above |
| S1 · contracted-only volumes | 42,000 cr | 105 | $13,825 | $34.42 | 5.4× | downside book: $1.45M outlays; financing $1.69/student-yr; still well under the SCC |
| S2 · CORSIA labeling never lands | sell voluntary $10/t | 322 | withdrawn | $40.21 | 4.6× | proceeds $1.29M against $2.35M outlays: net −$1.06M. The commercial reversal condition. |
| S3 · incidence low | 0.30 | 161 | $14,626 | $40.21 | 4.6× | — |
| S4 · incidence high | 1.20 | 644 | $3,656 | $40.21 | 4.6× | — |
| S5 · buy price $9.90 flat | $9.90 | 322 | $7,361 | $18.33 | 10.1× | outlays $2.37M: the model is insensitive to the buy-price path |
Recomputed, not asserted: the climate metric stays 5.4–10.2× below the social cost of carbon in every scenario, including the contracted-only downside. The fragile finding is commercial, not climatic: without the CORSIA label, the carbon layer runs a roughly $1.1M net loss at voluntary floor prices.
| Dimension | Rating | Assessment |
|---|---|---|
| Effect-size quality | The chain is cloned from the Rwanda model with zero Kenya-specific inputs: incidence, school water share, and severity mix are all pending. Preliminary is the ceiling until the Kenya burden lookup and any program evaluation data are traced. | |
| Counterfactual robustness | Another carbon developer could plausibly serve the partner; the counterfactual for Virridy's outlays is partner-funded replacement cycles at a slower cadence, not modeled in v1. The health-side counterfactual is not Virridy's to claim. | |
| Moral-weight transparency | All frameworks reported; ranking stable. The labeled cost basis, not the framework, is what drives interpretation. | |
| Attribution | The central caveat of the whole model: Virridy finances replacement cycles; the partner delivers and capitalizes the health impact. The $/DALY figure is dollars-through-the-carbon-layer per DALY in the system. Quoting it without that label is a misuse of the model. | |
| Excluded factors | Full delivery cost is unknown to this model (partner-borne). CORSIA labeling risk is real and priced in S2. The 2026 implied-students figure overstates that year because the credit figure includes an issuance backlog. | |
| Ranking stability | The climate metric is robust in every scenario (5.4–10.2× below the SCC, 7.3× integrity-adjusted). The commercially fragile finding is S2: CORSIA labeling is the reversal condition. |