# Water-loop teaching model

This is transparent accounting, not a habitat, treatment design, medical standard, or survival-time prediction.

For assigned clean-water throughput q litres per person per day, n people, d days and recovery fraction r:

- Total loop throughput: V = q × n × d
- Returned water: r × V
- Makeup needed for unrecovered throughput: (1 − r) × V

The interactive default uses 4 L/person/day, four people, 30 days and 90% recovery. The throughput is selected only to demonstrate arithmetic; it is not represented as an ISS consumption value. The 90% and 98% points are included for comparison with NASA system-level descriptions of station water-recovery capability and its later total-recovery milestone. Rates are hardware/configuration specific; the model does not assert that all uses or missions achieve either percentage.

## Exclusions

The model treats the same throughput as passing through the recovery loop every day and applies one constant recovery fraction. It omits water-quality limits, unavailable streams, leaks, reserve tanks, energy, filters, waste storage, oxygen, carbon dioxide, food, hygiene, microbial hazards, equipment mass, repair, resupply and failures. No conclusion about shelter endurance, safety, or the 500-day source claim follows.

## Primary sources

- NASA, Environmental Control and Life Support Systems: https://www.nasa.gov/reference/environmental-control-and-life-support-systems-eclss/ — water recovery, air revitalization and oxygen generation functions.
- NASA, 98% water recovery milestone: https://www.nasa.gov/missions/station/iss-research/nasa-achieves-water-recovery-milestone-on-international-space-station/ — station-specific total recovery milestone after brine processing.
- Williamson, Wilson & Luong, Status of ISS Water Management and Recovery, NASA NTRS, ICES-2024-317: https://ntrs.nasa.gov/citations/20240005472 — operational water-management subsystems.
- NASA, Human-Centered ECLSS Technical Brief: https://www.nasa.gov/wp-content/uploads/2023/07/eclss-technical-brief-ochmo.pdf — reliability and physiological/system context.

The diagram is an original conceptual resource map, not copied ISS hardware artwork.