Water H2O

spore: profile
id: water
spore_version: 0.2
family: water
name: Water
abbreviation: H2O
role: hydrogen-rich radiation shield and potable fluid
category: shielding
type: water-and-ice
summary: |
  Liquid water has a density of 999.79 kg/m3 at 0.028556 °C in the NIST saturation table, and it holds 4.2198 J/(g*K) of heat capacity at the same point. Water is 11.19% hydrogen by mass (calculated from NIST atomic weights). A 2013 NASA Langley analysis found that a single heavy-lift launch of water could protect astronauts for a 130-day deep-space mission before the 150 mSv design limit was exceeded, under the 1977 galactic cosmic ray environment. That result is an analysis, not a flight test. Water is also the potable water that the International Space Station stores and treats with biocides.
best_for: Hydrogen-rich shielding for crew areas that already hold potable water (NASA Langley analysis, 2013; ISS potable water practice, ICES 2023)
weakest_at: 'Freezing: water expands on freezing (PubChem), and stored water needs a biocide to stay free of microbes and biofilm (NASA ICES 2025)'
identity:
  formula: H2O
  cas: 7732-18-5
  source: pubchem-water
  where: Names and Identifiers (CID 962, CAS 7732-18-5); molecular formula H2O from the PubChem compound record
tags:
  environments:
    - deep-space
  stresses:
    - total-radiation-dose
  applications:
    - radiation-shielding
    - habitats-and-suits
properties:
  - benchmark: density
    label: Density of saturated liquid water near 0 °C
    value: 999.79
    unit: kg/m3
    scope: material
    conditions:
      state: saturated liquid
      temperature: 0.028556 °C (first printed row of the saturation table)
      pressure: 0.00061248 MPa (saturation pressure as printed)
    method: Value copied from the NIST Chemistry WebBook saturation table
    status: ground
    source: nist-sat
    where: Saturation properties table, row 1, Density (kg/m3) column
  - benchmark: density
    label: Density of liquid water at 0 °C/4 °C, PubChem
    value: 0.999868
    unit: g/cm3
    scope: material
    conditions:
      state: liquid
      basis: printed as 0.999868 at 0 °C/4 °C (liquid)
    method: Experimental density value printed in the PubChem record
    status: ground
    source: pubchem-water
    where: Chemical and Physical Properties, Experimental Properties, Density entry
  - benchmark: density
    label: Density of liquid water at 25 °C, PubChem
    value: 0.995
    unit: g/cm3
    scope: material
    conditions:
      state: liquid
      temperature: 25 °C
    method: Experimental density value printed in the PubChem record
    status: ground
    note: The 25 °C figure was not checked against a second source. It is lower than the NIST value near 0 °C, and the two temperatures differ, so they are not compared directly.
    source: pubchem-water
    where: Chemical and Physical Properties, Experimental Properties, Density entry (first value)
  - benchmark: density
    label: Density of ice at 0 °C
    value: 0.917
    unit: g/cm3
    scope: material
    conditions:
      phase: ice
      temperature: 0 °C
    method: Experimental density value printed in the PubChem record
    status: ground
    source: pubchem-water
    where: Chemical and Physical Properties, Experimental Properties, Density entry (ice value)
  - benchmark: melting_point
    label: Melting point of ice and water
    value: 0
    unit: °C
    scope: material
    conditions:
      pressure: not stated in the source
    method: Value printed in the PubChem experimental melting point entry
    status: ground
    source: pubchem-water
    where: Chemical and Physical Properties, Experimental Properties, Melting Point
  - benchmark: boiling_point
    label: Boiling point, PubChem
    value: 99.974
    unit: °C
    scope: material
    conditions:
      pressure: not stated for this value; the same PubChem record gives 212 °F at 760 mmHg
    method: Value printed in the PubChem experimental boiling point entry
    status: ground
    source: pubchem-water
    where: Chemical and Physical Properties, Experimental Properties, Boiling Point
  - benchmark: boiling_point
    label: Boiling point, NIST average
    value: 373.17
    unit: K
    scope: material
    conditions:
      pressure: not stated on the page
      uncertainty: ±0.04 K, average of 7 values
    method: Value printed in the NIST phase change data
    status: ground
    note: NIST gives 373.17 K, which is about 0.05 °C above the PubChem value of 99.974 °C. Both are kept as printed.
    source: nist-webbook
    where: Phase change data, Tboil
  - benchmark: critical_temperature
    label: Critical temperature, NIST average
    value: 647
    unit: K
    scope: material
    conditions:
      uncertainty: ±2 K, average of 7 values
    method: Value printed in the NIST phase change data
    status: ground
    source: nist-webbook
    where: Phase change data, Tc
  - benchmark: critical_temperature
    label: Critical temperature, PubChem
    value: 374.2
    unit: °C
    scope: material
    conditions:
      basis: printed in the PubChem safety and hazard properties section
    method: Value printed in the PubChem record
    status: ground
    note: The PubChem value of 374.2 °C differs from the NIST value of 647 K (about 373.9 °C). Both are kept as printed.
    source: pubchem-water
    where: Safety and Hazards, Safety and Hazard Properties, Critical Temperature and Pressure
  - benchmark: critical_pressure
    label: Critical pressure, NIST
    value: 220.64
    unit: bar
    scope: material
    conditions:
      basis: NIST gives the value from Sato, Watanabe et al. (1991); other sources in the NIST table list 220.60, 220.46 and 220.64 bar
    method: Value printed in the NIST phase change data
    status: ground
    source: nist-webbook
    where: Phase change data, Pc
  - benchmark: critical_pressure
    label: Critical pressure, PubChem
    value: 218
    unit: atm
    scope: material
    conditions:
      basis: printed in the PubChem safety and hazard properties section
    method: Value printed in the PubChem record
    status: ground
    note: The PubChem value of 218 atm differs from the NIST value of 220.64 bar (about 217.8 atm). Both are kept as printed.
    source: pubchem-water
    where: Safety and Hazards, Safety and Hazard Properties, Critical Temperature and Pressure
  - benchmark: specific_heat
    label: Isobaric heat capacity of saturated liquid water near 0 °C
    value: 4.2198
    unit: J/(g*K)
    scope: material
    conditions:
      state: saturated liquid
      temperature: 0.028556 °C (first printed row)
      pressure: saturation
    method: Value copied from the NIST saturation table, Cp column
    status: ground
    source: nist-sat
    where: Saturation properties table, row 1, Cp (J/g*K) column
  - benchmark: dynamic_viscosity
    label: Dynamic viscosity of saturated liquid water near 0 °C
    value: 1790.2
    unit: uPa*s
    scope: material
    conditions:
      state: saturated liquid
      temperature: 0.028556 °C (first printed row)
    method: Value copied from the NIST saturation table, Viscosity column
    status: ground
    note: Snake-case name; this property is not in spores/property-canon.yaml.
    source: nist-sat
    where: Saturation properties table, row 1, Viscosity (uPa*s) column
  - benchmark: surface_tension
    label: Surface tension of water at 25 °C
    value: 71.97
    unit: dyne/cm
    scope: material
    conditions:
      temperature: 25 °C
    method: Value printed in the PubChem experimental surface tension entry
    status: ground
    source: pubchem-water
    where: Chemical and Physical Properties, Experimental Properties, Surface Tension
  - benchmark: vapor_pressure
    label: Vapor pressure of water at 273.16 K
    value: 611.657
    unit: Pa
    scope: material
    conditions:
      temperature: 273.16 K
    method: Value printed in the PubChem experimental vapor pressure entry
    status: ground
    note: Snake-case name; this property is not in spores/property-canon.yaml.
    source: pubchem-water
    where: 'Chemical and Physical Properties, Experimental Properties, Vapor Pressure (VP: 611.657 Pa at 273.16 K)'
  - benchmark: refractive_index
    label: Refractive index of water
    value: 1.333
    unit: '-'
    scope: material
    conditions:
      temperature: not stated in the source
      wavelength: not stated in the source
    method: Value printed in the PubChem refractive index entry
    status: ground
    source: pubchem-water
    where: Chemical and Physical Properties, Experimental Properties, Refractive Index
  - benchmark: temperature_of_max_density
    label: Temperature of maximum density of liquid water
    value: 3.98
    unit: °C
    scope: material
    conditions:
      basis: printed as the temperature of maximum density in the PubChem density entry
    method: Value printed in the PubChem record
    status: ground
    note: Snake-case name; this property is not in spores/property-canon.yaml.
    source: pubchem-water
    where: Chemical and Physical Properties, Experimental Properties, Density entry (Temp of max density 3.98 °C)
  - benchmark: hydrogen_mass_fraction
    label: Hydrogen share of the mass of water
    value: 11.19
    unit: '%'
    scope: material
    conditions:
      basis: 2 hydrogen atoms in H2O divided by the molecular weight 18.015 g/mol, with hydrogen taken as 1.008 g/mol
    method: 'Calculated by Space Mushroom: 2 x 1.008 / 18.015 = 11.19%. The NIST atomic weight of hydrogen is printed as the interval [1.007 84, 1.008 11], which gives the same 11.19% to two decimals.'
    status: calculated
    note: Snake-case name; this property is not in spores/property-canon.yaml.
    source: nist-atomic
    where: Standard atomic weight table, H row (interval printed); PubChem molecular weight 18.015 g/mol
  - benchmark: protection_time
    label: Protection time from a single heavy-lift launch of water
    value: 130
    unit: days
    scope: material
    conditions:
      environment: 1977 galactic cosmic ray environment
      exposure_limit: 150 mSv design basis
      launch: single heavy-lift launch of pure shielding mass, under the paper's assumptions
    method: Analysis result stated in the paper abstract; not a measurement
    status: calculated
    note: Snake-case name; this property is not in spores/property-canon.yaml. The same abstract gives 160 days for liquid hydrogen and says a single launch of polyethylene gives the same 130 days. The same abstract also says that liquid hydrogen is not the best shield per unit mass compared with polyethylene for missions longer than 225 days.
    source: singleterry2013
    where: Abstract
corrosion:
  - environment: Potable water held in spacecraft storage and distribution lines (microbial growth)
    headline: Stored potable water needs a biocide to control microbes, biofilm and microbially influenced corrosion.
    effect: NASA's 2025 ICES paper states that a potable-water biocide should prevent or control microbial growth, prevent or limit biofilm formation, and prevent microbiologically influenced corrosion. The target dose is 200 to 400 parts per billion of silver ion (Ag+), chosen with the Spacecraft Water Exposure Guidelines for 1000-day missions as the upper limit.
    rating: moderate
    conditions:
      biocide: silver ion (Ag+)
      target_range: 200 to 400 ppb Ag+
      basis: upper limit set by the Spacecraft Water Exposure Guidelines for 1000-day missions
    source: irwin2025
    where: Introduction, requirements paragraph; Silver biocide section, target range paragraph
  - environment: Iodine-disinfected potable water on the International Space Station
    headline: Iodine must be removed at the dispenser before crew consumption; silver does not need removal.
    effect: NASA's 2025 ICES paper states that, unlike iodine, silver ion biocide does not need to be removed at the potable water dispenser, and that Ag+ is effective at levels below 400 ppb that are safe for human consumption. The 2023 ICES paper compares iodine and silver for ISS potable water and identifies gaps in knowledge.
    rating: low
    conditions:
      biocide: molecular iodine (ISS) versus silver ion (Ag+)
    source: irwin2025
    where: Silver biocide introduction paragraph
uses:
  - application: radiation-shielding
    device: Deep-space crew shielding (analysis only)
    example: A NASA Langley analysis found that a single heavy-lift launch of water or polyethylene could protect astronauts for a 130-day mission before exceeding the 150 mSv design basis exposure, under the 1977 galactic cosmic ray environment.
    source: singleterry2013
    where: Abstract
  - application: radiation-shielding
    device: Deep-space vehicle with permanent on-board water storage (modelling thesis)
    example: A 2018 Cal Poly master's thesis on utilizing permanent on-board water storage for deep-space radiation shielding concludes that the permanent inclusion of water gives added support against galactic cosmic rays and solar particle events; the abstract gives no numbers.
    source: gehrke2018
    where: Abstract (title and conclusion)
  - application: habitats-and-suits
    device: International Space Station potable water system (drinking, hygiene and technical water)
    example: Molecular iodine and ionic silver have been used on the International Space Station for decades to control microbes in potable water, and the 2023 ICES paper compares the two biocides for drinking, hygiene, technical, oxygen-generation and extravehicular activity water.
    source: muirhead2023
    where: Abstract
supply:
  - subject: Water (H2O), abundance on Earth
    abundance: About 1,386 million km3 (332.5 million mi3) of water on Earth; the oceans hold about 96.5% of it (USGS). Of freshwater, over 68% is in ice and glaciers, and about 30% is in the ground (USGS).
    producers: []
    critical_lists: []
    recycling: Not found in any source we hold.
    substitutes: []
    source: usgs-water
    where: 'How much water is there on Earth: Overview; Where is Earth''s water located; data table (percent of freshwater)'
documents:
  - title: 'NIST Chemistry WebBook: water, saturation and phase change data'
    type: database
    url: https://webbook.nist.gov/cgi/cbook.cgi?ID=C7732185&Units=SI&Mask=4#Thermo-Phase
    year: 2026
  - title: 'NIST Chemistry WebBook: water, saturation properties table'
    type: database
    url: https://webbook.nist.gov/cgi/fluid.cgi?ID=C7732185&Type=SatT&Digits=5&PLow=&PHigh=&PInc=&T=25&RefState=DEF&TUnit=C&PUnit=MPa&DUnit=kg%2Fm3&HUnit=kJ%2Fkg&WUnit=m%2Fs&VisUnit=uPa*s&STUnit=N%2Fm&Action=Load
    year: 2026
  - title: 'NIST atomic weights: hydrogen and oxygen'
    type: database
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=H&all=all&ascii=html&isotype=some
    year: 2026
  - title: 'PubChem: Water (CID 962)'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/Water
    year: 2026
  - title: Singleterry, Radiation Engineering Analysis of Shielding Materials (NASA Langley; Acta Astronautica 91, 2013)
    type: paper
    url: https://ntrs.nasa.gov/citations/20140003150
    year: 2013
  - title: 'Irwin et al., Silver Foam: Long-Term Passive Dosing of Biocide, Update 2025 (ICES-2025-194)'
    type: paper
    url: https://ntrs.nasa.gov/api/citations/20250005545/downloads/ICES-2025-194.pdf
    year: 2025
  - title: Muirhead et al., Evaluation of Iodine and Silver as Biocides for Potable Water (ICES 2023)
    type: paper
    url: https://ntrs.nasa.gov/api/citations/20220015620/downloads/ICES%202023%20Abstract%20Iodine%20and%20Silver%20for%20Strives.pdf
    year: 2023
  - title: Gehrke, Utilizing Permanent On-Board Water Storage for Efficient Deep Space Radiation Shielding (Cal Poly thesis)
    type: paper
    url: https://digitalcommons.calpoly.edu/theses/1933
    year: 2018
  - title: 'USGS Water Science School: How much water is there on Earth?'
    type: report
    url: https://www.usgs.gov/special-topics/water-science-school/science/how-much-water-there-earth
    year: 2026
gaps:
  - No flight or space-environment measurement of water as a radiation shield was found in the sources read here. The 130-day figure is an analysis result from one 2013 paper, and only its abstract was read.
  - No neutron or galactic cosmic ray dose per unit areal density for water was read from a page. The NIST table covers photons (X-ray and gamma) only.
  - The Cal Poly thesis PDF returned HTTP 403 when downloaded, so only its abstract was read. Its Orion-related modelling numbers are not in this profile.
  - 'Supply: water is not a mined commodity. No producer shares, critical-mineral listing or recycling figure for water was found in a source we hold; the USGS mineral chapters do not cover it.'
  - No room-temperature (20 to 25 °C) liquid density, heat capacity or viscosity from NIST was read. The fetched NIST saturation table printed its first saturated-liquid row at 0.028556 °C, and the 25 °C value was not in the copy we read.
  - NIST liquid thermal conductivity in the saturation table (0.55565 W/(m*K) in row 1) was left out because no second source for it was read in this run.
  - Ice properties beyond density (heat of fusion, thermal conductivity, expansion coefficient) were not read from a source.
  - Critical temperature and pressure disagree between NIST and PubChem; both are kept as printed, and neither was checked against a third source.
  - Biocide depletion over the storage life of stored water was not read on a fetched page and is not stated here.
  - Freezing damage to tanks or lines has no test result in any source read here; the damage risk is an inference from the PubChem note that water expands on freezing.
  - Hazard data rest on the PubChem record (aggregated ECHA notifications). No supplier safety data sheet for water was read.
  - 'Snake-case names used for properties not in spores/property-canon.yaml: dynamic_viscosity, vapor_pressure, temperature_of_max_density, hydrogen_mass_fraction, protection_time, critical_temperature and critical_pressure (the last two may already be aliases; check before import).'
  - No media, images or CSV added in this profile.
sources:
  nist-sat:
    title: 'NIST Chemistry WebBook, water: saturation properties table'
    id: NIST SRD 69; CAS 7732-18-5
    url: https://webbook.nist.gov/cgi/fluid.cgi?ID=C7732185&Type=SatT&Digits=5&PLow=&PHigh=&PInc=&T=25&RefState=DEF&TUnit=C&PUnit=MPa&DUnit=kg%2Fm3&HUnit=kJ%2Fkg&WUnit=m%2Fs&VisUnit=uPa*s&STUnit=N%2Fm&Action=Load
    year: 2026
    kind: database
    license: US government work (NIST)
  nist-webbook:
    title: 'NIST Chemistry WebBook, water: phase change data'
    id: NIST SRD 69; CAS 7732-18-5
    url: https://webbook.nist.gov/cgi/cbook.cgi?ID=C7732185&Units=SI&Mask=4#Thermo-Phase
    year: 2026
    kind: database
    license: US government work (NIST)
  nist-atomic:
    title: 'Atomic weights and isotopic compositions: hydrogen and oxygen (NIST)'
    id: NIST standard atomic weights
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=H&all=all&ascii=html&isotype=some
    year: 2026
    kind: database
    license: US government work (NIST)
  pubchem-water:
    title: 'PubChem compound record: Water (CID 962)'
    id: CID 962; CAS 7732-18-5
    url: https://pubchem.ncbi.nlm.nih.gov/compound/Water
    year: 2026
    kind: database
    license: public domain (NCBI)
  usgs-water:
    title: 'USGS Water Science School: How much water is there on Earth?'
    id: USGS Water Science School
    url: https://www.usgs.gov/special-topics/water-science-school/science/how-much-water-there-earth
    year: 2026
    kind: web
    license: public domain (USGS)
  singleterry2013:
    title: Radiation Engineering Analysis of Shielding Materials to Assess Their Ability to Protect Astronauts in Deep Space From Energetic Particle Radiation
    id: NTRS 20140003150; doi:10.1016/j.actaastro.2013.04.013 (Acta Astronautica 91)
    url: https://ntrs.nasa.gov/citations/20140003150
    year: 2013
    kind: paper
    license: public domain (NASA)
  irwin2025:
    title: 'Silver Foam: A Novel Approach for Long-Term Passive Dosing of Biocide in Spacecraft Potable Water Systems, Update 2025 (ICES-2025-194)'
    id: ICES-2025-194; NTRS 20250005545
    url: https://ntrs.nasa.gov/api/citations/20250005545/downloads/ICES-2025-194.pdf
    year: 2025
    kind: paper
    license: public domain (NASA)
  muirhead2023:
    title: Evaluation of Iodine and Silver as Biocides for Potable Water in Human Missions beyond Low Earth Orbit (ICES 2023)
    id: NTRS 20220015620
    url: https://ntrs.nasa.gov/api/citations/20220015620/downloads/ICES%202023%20Abstract%20Iodine%20and%20Silver%20for%20Strives.pdf
    year: 2023
    kind: paper
    license: public domain (NASA)
  gehrke2018:
    title: Utilizing Permanent On-Board Water Storage for Efficient Deep Space Radiation Shielding
    id: Cal Poly master's thesis, 2018 (Nathan Ryan Gehrke); abstract read
    url: https://digitalcommons.calpoly.edu/theses/1933
    year: 2018
    kind: paper
    license: thesis (Cal Poly digital commons)
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 19
  unreachable: 12
  caveats: 3
  note: Written by an AI assistant on 2026-11-01 from NIST, PubChem, USGS and NASA pages read in that run. The Cal Poly thesis PDF was not readable (HTTP 403); its abstract was read. verify-values run on 2026-11-01, 7 values found in the source text, 12 not checkable by the verifier (their pages were not readable by it; those values were read by hand in this run), 0 not found.
risks:
  hazards:
    - text: PubChem reports that water does not meet GHS hazard criteria in 1,866 of 1,876 company reports (99.5%); the record's aggregated ECHA notifications give the same picture.
      source: pubchem-water
      where: Safety and Hazards, GHS Classification (note line)
    - text: PubChem's health-hazard section states that water itself is nontoxic; hazards come from substances dissolved in it.
      source: pubchem-water
      where: Safety and Hazards, Hazards Identification, Health Hazards
  failure_risks:
    - mode: Freezing of stored water
      trigger: Temperature at or below 0 °C
      consequence: PubChem notes that water expands on freezing; its ice density is 0.917 g/cm3 at 0 °C. Damage to tanks or lines is not measured in any source read here.
      severity: moderate
      source: pubchem-water
      where: Chemical and Physical Properties, Density entry
    - mode: Microbial growth in stored potable water
      trigger: Storage without an effective biocide
      consequence: NASA's 2025 ICES paper lists microbial growth, biofilm and microbially influenced corrosion as what a potable-water biocide must prevent.
      severity: moderate
      source: irwin2025
      where: Introduction, requirements paragraph
  side_effects:
    - text: NASA's 2025 ICES paper notes that, unlike silver, iodine must be removed at the potable water dispenser before crew consumption.
      affects: Crew drinking water at the dispenser
      source: irwin2025
      where: Silver biocide introduction paragraph
  handling:
    - text: Keep stored potable water treated with a biocide; NASA's 2025 requirements call for control of microbes and biofilm.
      source: irwin2025
      where: Introduction, requirements paragraph
    - text: Keep stored water from freezing, because it expands when it freezes (PubChem).
      source: pubchem-water
      where: Chemical and Physical Properties, Density entry
  mitigations:
    - text: Silver ion biocide is targeted at 200 to 400 ppb; unlike iodine, silver needs no removal at the dispenser.
      source: irwin2025
      where: Silver biocide section, target range paragraph
story:
  recipe:
    line: 'Water is H2O: one oxygen atom bonded covalently to two hydrogen atoms (PubChem, CAS 7732-18-5). Its molecular weight is 18.015 g/mol (PubChem). Water is not mined; it is the liquid that the shield and the potable water system store.'
    parts:
      - name: Hydrogen
        symbol: H
        role: Two hydrogen atoms per molecule. Hydrogen makes up 11.19% of the mass of water (calculated; see properties). NIST prints the standard atomic weight of hydrogen as an interval, so no single value is given here.
      - name: Oxygen
        symbol: O
        role: One oxygen atom per molecule; the rest of the mass of water. NIST prints the standard atomic weight of oxygen as an interval, so no single value is given here.
  risk_groups:
    - title: For people
      level: 0
      verdict: Not classified hazardous
      lead: 'Water is not classified as hazardous in the PubChem record: 1,866 of 1,876 company reports (99.5%) say it does not meet GHS hazard criteria.'
      points:
        - label: The liquid
          line: PubChem's health-hazard section says that water itself is nontoxic. Hazards come from substances dissolved in it, which have their own records.
        - label: Biological growth
          line: Stored water needs a biocide to control microbes, biofilm and microbially influenced corrosion, according to NASA's 2025 ICES paper.
    - title: If water freezes in a shield or line
      lead: Freezing is a physical hazard for stored water. No source read here tests what it does to a tank.
      points:
        - label: Expansion
          line: PubChem notes that water expands on freezing. Its ice density is 0.917 g/cm3 at 0 °C, while liquid water is 0.999868 g/cm3 at 0 °C/4 °C.
        - label: Damage
          line: Damage to tanks or lines from freezing is an inference from the expansion note. No test in the sources read here measured it.
    - title: Handling and storage
      points:
        - label: Biocide
          line: NASA's 2025 ICES paper targets 200 to 400 ppb of silver ion (Ag+) for stored potable water, and states that Ag+ is effective below 400 ppb and safe for human consumption at that level.
        - label: Iodine
          line: Unlike silver, iodine must be removed at the potable water dispenser before crew consumption, according to the same 2025 paper.
  why: Water is a hydrogen-rich material that the International Space Station already stores as potable water (ICES 2023). A 2013 NASA Langley analysis found that a single heavy-lift launch of water could protect astronauts for a 130-day deep-space mission under its assumptions, the same as polyethylene. A 2018 Cal Poly thesis concludes that permanent on-board water storage adds protection against galactic cosmic rays and solar particle events; its abstract gives no numbers. The shielding figures are analysis results, not flight measurements.
  uses:
    - where: Deep-space crew shielding (analysis)
      line: A NASA Langley analysis found that a single heavy-lift launch of water could protect astronauts for a 130-day mission before the 150 mSv design basis was exceeded, under the 1977 galactic cosmic ray environment.
    - where: Potable water on the International Space Station
      line: Iodine and silver biocides have been used on the International Space Station to control microbes in potable water. A 2023 ICES paper compares them for drinking, hygiene, technical, oxygen-generation and extravehicular activity water.
  can_do:
    - label: Radiation shielding
      benchmark: protection_time
      value: 130 days
      line: A single heavy-lift launch of water can protect astronauts for a 130-day mission under the 1977 galactic cosmic ray environment, before the 150 mSv design basis is exceeded (NASA Langley analysis, 2013).
    - label: Heat capacity
      benchmark: specific_heat
      value: 4.2198 J/(g*K)
      line: Saturated liquid water has an isobaric heat capacity of 4.2198 J/(g*K) at 0.028556 °C, per the NIST saturation table.
    - label: Liquid range at 1 atm
      value: 0 °C to 99.974 °C
      line: Liquid water runs from its melting point of 0 °C to its boiling point of 99.974 °C, as printed by PubChem; the record gives the boiling point without its pressure, and the same record gives 212 °F at 760 mmHg.
  compare: Per launch, the 2013 NASA Langley analysis finds that water and polyethylene protect astronauts for the same 130-day mission under its assumptions. The same abstract gives 160 days for liquid hydrogen and says that liquid hydrogen is not the best shield per unit mass compared with polyethylene for missions longer than 225 days. These are analysis results for the 1977 galactic cosmic ray environment, not measurements. The NIST table gives only the photon (X-ray and gamma) attenuation of water, so it does not show how water compares for galactic cosmic rays.
  compare_rows:
    - label: Density, liquid near 0 °C
      benchmark: density
    - label: Hydrogen mass fraction
      benchmark: hydrogen_mass_fraction
  handling:
    - Keep stored potable water treated with a biocide; NASA's 2025 requirements call for control of microbes and biofilm.
    - Keep water from freezing in a shield or line, because it expands when it freezes (PubChem).
    - Silver ion biocide is targeted at 200 to 400 ppb; unlike iodine, silver needs no removal at the dispenser (ICES 2025).
  good_for:
    - Hydrogen-rich shielding in crew areas where potable water is already stored (NASA Langley, 2013; ICES 2023).
    - 'A well-characterised heat capacity: 4.2198 J/(g*K) for saturated liquid near 0 °C (NIST).'
  watch_out:
    - 'Freezing: water expands when it freezes (PubChem), and no source read here tests what that does to a tank.'
    - 'Biological growth: stored water needs a biocide (NASA ICES 2025).'
    - The 130-day protection figure is a 2013 analysis under stated assumptions, not a flight test.
  verdict: Water is a practical hydrogen-rich shield for crew areas that already hold potable water. Its shielding value rests on a 2013 analysis, not on a flight test, and it must be kept from freezing and from microbes.