Rainwater Collection for Emergency Preparedness

Rainwater collection provides a renewable water source that does not depend on municipal systems or groundwater. During extended emergencies when stored water runs out and normal supplies are unavailable, the ability to capture and use rainwater can be invaluable.

A basic rainwater collection system can be as simple as placing containers outside during rain, or as sophisticated as a whole house system with filtration and pressurized delivery. For emergency preparedness, even simple setups can provide significant water security.

This guide covers the fundamentals of rainwater harvesting, from calculating potential yield to treatment requirements for safe use. Understanding these basics helps you evaluate whether rainwater collection makes sense for your situation.

Calculating Collection Potential

The amount of rainwater you can collect depends on your catchment area (usually roof space) and local rainfall. A simple formula provides estimates:

Gallons collected = Roof square footage x Rainfall inches x 0.623

For example, a 1,000 square foot roof section receiving 1 inch of rain yields approximately 623 gallons. Even modest rainfall on a standard roof produces substantial water volumes.

Collection efficiency varies. You typically capture 75 to 90 percent of theoretical yield after accounting for evaporation, splash, and system losses. First flush diverters that discard initial runoff reduce yield further but improve water quality.

Regional Considerations

Annual rainfall varies dramatically by location. The Pacific Northwest might receive 40 or more inches annually while desert Southwest regions see less than 10 inches. Check historical rainfall data for your area to estimate realistic annual collection potential.

Rainfall distribution matters too. Areas with steady year round precipitation offer more reliable collection than regions with distinct wet and dry seasons.

Basic Collection Methods

Simple Container Collection

The most basic approach places containers outside to catch rain directly. This works for emergency situations but collects limited volume. Food grade buckets, trash cans with lids, or any clean container can serve this purpose.

Tarp and Funnel Systems

Stretching a tarp between supports creates an improvised catchment area. The tarp funnels water to a collection point. This portable method works for camping, evacuation situations, or supplementing other collection.

Roof Runoff Collection

Most rainwater systems capture roof runoff via gutters and downspouts. A standard rain barrel placed under a downspout can collect 50 to 100 gallons from a single rain event. Multiple barrels linked together increase capacity.

Dedicated Catchment Surfaces

Purpose built catchment surfaces using food safe materials provide cleaner water than roof runoff. Metal or plastic panels angled toward collection points work well for systems where water quality is critical.

Storage Options

Rain Barrels (50 to 100 gallons)

Standard rain barrels are affordable and fit most residential situations. They connect directly to downspouts and include spigots for water access. Multiple barrels can be linked in series for increased capacity.

IBC Totes (275 gallons)

Intermediate Bulk Containers offer more capacity while remaining relatively affordable. Used food grade totes are often available from industrial suppliers. They require more space but provide substantial storage.

Cisterns and Large Tanks (500+ gallons)

Dedicated water storage tanks offer the largest capacity. Above ground plastic tanks range from 500 to several thousand gallons. Underground cisterns provide even larger storage while preserving yard space.

Storage Considerations

All rainwater storage should be opaque or kept dark to prevent algae growth. Screens over inlets keep debris and insects out. Overflow outlets prevent tank damage during heavy rain. First flush diverters improve water quality by discarding initial dirty runoff.

Water Quality and Treatment

Rainwater quality varies based on catchment surface, atmospheric conditions, and storage methods. Fresh rainwater is relatively pure but picks up contaminants from roofs, gutters, and storage systems.

Roof Material Concerns

Asphalt shingles can leach chemicals and shed granules. Metal roofing is generally cleanest for rainwater collection. Avoid collecting from roofs with lead flashing, treated wood, or recent tar application. First flush systems help by discarding initial contaminated runoff.

Treatment for Drinking

Rainwater intended for drinking should be filtered and disinfected. A basic treatment train includes: sediment pre filtration, carbon filtration for chemicals and taste, fine filtration (0.2 micron or better) for bacteria and protozoa, and UV or chemical disinfection for viruses.

For emergency use, boiling rainwater provides effective treatment against biological contaminants. Chemical treatment with bleach also works well for collected rainwater.

Non Potable Uses

Untreated rainwater is suitable for many uses: garden watering, toilet flushing, laundry, cleaning, and fire suppression. Reserving rainwater for non potable uses while keeping stored treated water for drinking extends your overall water security.

Legal Considerations

Rainwater collection regulations vary by location. Most US states allow residential rainwater collection, but some have restrictions or permit requirements.

Colorado historically restricted rainwater collection but now allows limited residential harvesting. Utah requires registration for larger systems. Most states have no restrictions on residential collection.

Check your state and local regulations before installing permanent collection systems. Temporary emergency collection typically falls outside regulatory frameworks.

Some homeowners associations have rules about rain barrels and outdoor storage. Review HOA guidelines if applicable to your property.

Emergency Collection Setup

You can improvise rainwater collection quickly when emergencies arise:

Immediate actions: Place all available containers outside when rain is forecast. Position containers under roof edges, eaves, or anywhere water concentrates during rain.

Tarp collection: Secure a clean tarp at an angle directing water to a container. Even a small tarp significantly increases collection area.

Gutter modification: If you have gutters but no rain barrel, disconnect a downspout and direct flow into containers. Use a funnel or improvised diverter.

Treatment plan: Assume all collected rainwater needs treatment before drinking. Have filtration and disinfection supplies ready.

Quick Reference Checklist

• Research local regulations on rainwater collection
• Assess roof material and condition for collection suitability
• Calculate potential yield from available catchment area
• Choose storage capacity based on needs and space
• Install screens and first flush diverters for quality
• Plan treatment methods for intended water uses
• Keep emergency collection supplies ready (tarps, containers)
• Maintain system: clean gutters, check screens, inspect storage