Water Source Risk Matrix

Risk Factor Assessment

Before treating any water, assess the risk level. Higher risk = more layers of treatment.

Risk Increases With:

Proximity to contamination:

• Upstream human activity (towns, farms, campsites)
• Downstream from sewage outfalls or septic systems
• Near livestock or wildlife concentration (beaver ponds, cattle grazing)
• Within 100 feet of privies, latrines, or pit toilets
• In flood zones with potential sewage contamination

Water characteristics:

• Visibly turbid or colored
• Unusual odor (sulfur, petroleum, chemical)
• Dead animals in or near water
• Algal bloom present (green, blue-green, or red color)
• Standing water vs. flowing water
• Warm water (bacteria multiply faster)

Environmental context:

• Post-disaster conditions (flooding, earthquake disrupting sewage)
• Industrial area (chemical contamination risk)
• Agricultural area (nitrate runoff, pesticide contamination)
• Urban environment (heavy metals, petroleum products)

Risk Decreases With:

• High elevation, remote location, no upstream human activity
• Fast-moving, well-oxygenated water
• Clear water with good visibility
• Spring source (groundwater filtered through rock and soil)
• Known clean history and recent testing
• Cold temperatures

The Risk Matrix

Level 1 — Very Low Risk (Standard Precaution Only)

Sources:

• Municipal tap water (grid functioning, no pressure loss)
• Commercially bottled water
• Recently tested private well with clean results

Treatment: None required for ongoing use. Boil or treat if any of the above status changes.

Indicators of status change: Tap water appears cloudy or colored, tastes or smells different, municipal boil advisory issued, pressure loss or extended outage.

Level 2 — Low-Moderate Risk (Basic Treatment)

Sources:

• Municipal tap water after brief outage (pressure failure allows contaminant entry)
• Well water without recent testing
• Spring water from remote, undisturbed area
• High-elevation stream water, no upstream human use

Treatment: Boiling (1 minute) OR chemical disinfection (chlorine/iodine at standard dose) OR UV treatment

What this addresses: Bacteria, viruses, protozoa — the typical suite of biological pathogens

What this may miss: Chemical contamination (not relevant at Level 2, generally)

Level 3 — Moderate Risk (Standard Full Treatment)

Sources:

• Surface streams near hiking trails, campsites
• Lowland streams without known upstream contamination
• Lake water from remote area
• Rainwater collected from clean roof with first flush

Treatment required: Hollow fiber filter (removes bacteria and protozoa) + chemical disinfection or UV (addresses viruses)

For turbid water: Pre-filter through cloth before hollow fiber

Level 4 — High Risk (Comprehensive Treatment)

Sources:

• Water downstream from agricultural areas
• Streams near cattle grazing (Cryptosporidium and Giardia)
• Beaver habitat water (Giardia strongly associated)
• Lake water from developed recreation area
• Urban water during crisis
• Roof runoff without first flush

Treatment required: Settle + pre-filter → hollow fiber → activated carbon → chlorine dioxide (full 4-hour contact for Crypto) OR hollow fiber → UV

Why more treatment: Higher pathogen diversity and load, possible chemical contamination from agricultural runoff

Level 5 — Very High Risk (Full Treatment or Avoid)

Sources:

• Flood water
• Water with obvious sewage contamination
• Downstream from sewage outfall
• Water with dead animals present
• Water with petroleum or chemical sheen or odor

Treatment required: Settle + sediment filter → activated carbon (if chemical) → hollow fiber → chemical disinfection

Strong recommendation: If any better water source is available, use it. Level 5 sources require multiple treatment stages and may still harbor contaminants not fully addressed by field methods.

Not Potable — Distillation or Avoid

Sources:

• Seawater
• Brackish water
• Water with confirmed heavy chemical contamination (fuel spill, industrial discharge)
• Water with algal bloom

No standard filtration or disinfection method removes dissolved salt, heavy metals, or cyanobacterial toxins. Distillation addresses dissolved salts and most chemicals. Algal toxins: avoid these sources.

Post-Disaster Water Risk Escalation

During grid-down scenarios, water sources that were previously safe may become contaminated.

Municipal tap water: If pressure fails (power outage stops pumps), contaminants can be drawn backward into distribution lines. Treat as Level 3 until normal pressure is restored and a boil advisory is issued and lifted.

Well water: Flooding can contaminate shallow wells. If your well was flooded, treat as Level 5 until tested. Disinfect the well (shock chlorination) before use.

Previously safe surface water: Post-disaster conditions (damaged sewage infrastructure, animal mortality events, agricultural flooding) can suddenly elevate the risk of previously clean-testing water. When disaster conditions are present, escalate all source risk levels by one category.

Quick Decision Guide

You have treated/stored water: Use it first. Don't take risks with unknown sources while known-safe water exists.

You need to use an untreated source: Identify the source type, apply the risk matrix, use the appropriate treatment level.

You have limited treatment resources: Prioritize treatment levels. Use boiling (requires fire) for highest-risk sources. Use chemical treatment for lower-risk sources where you want to conserve fuel. Use hollow fiber filter (reusable, no consumables) for backup.

You have no treatment resources: Highest-quality source available (spring over stream, upstream over downstream), boil only if fire is available. SODIS if fire is not. These are fallback options, not ideals.