A dark garden hose left in the sun can become surprisingly warm.

A copper solar collector applies the same basic principle more deliberately. Water passes through dark copper tubing mounted inside a shallow insulated box. A transparent cover admits sunlight while limiting heat loss from moving air.

As the copper absorbs solar energy, it transfers heat into the water.

The result can be useful for:

Preheating water for outdoor washing
Warming water for a gravity-fed camp shower
Cleaning garden tools
Washing equipment at an off-grid property
Demonstrating solar-thermal energy
Reducing the energy needed for a later heating step
Producing limited warm water during an outage

However, this homemade collector should not be treated as a complete residential water heater.

A code-compliant domestic solar-water system may include storage tanks, pumps, controllers, heat exchangers, freeze protection, pressure control, temperature-and-pressure relief valves, tempering valves, backflow protection, and professionally selected piping. Certified collectors and complete systems are evaluated separately because the safety and performance of the entire installation depend on far more than the collector panel alone. (SWS)

The project in this guide remains:

Ground-mounted
Gravity-fed
Open to atmospheric pressure
Separate from household plumbing
Continuously supervised while heating
Drained after use

That makes it much easier to test without creating a pressurized container of uncontrolled hot water.

How the Solar Collector Works

The system has four main parts:

1. Vented supply container

A clean water container sits slightly above the collector and feeds it by gravity.

2. Glazed copper collector

Sunlight heats blackened copper tubing inside an insulated enclosure.

3. Open warm-water outlet

The collector outlet remains open and drains into a second vented container.

4. Mixing and use container

The solar-heated water is measured and mixed with cooler water before use.

The complete water path is:

Vented cold-water tank → lower collector inlet → upper collector outlet → open receiving container

The outlet must never be closed while the collector contains water and is exposed to sunlight.

Heating trapped liquid can create thermal expansion and dangerous pressure. Residential solar-water systems require pressure-relief and temperature-control provisions selected according to applicable codes and manufacturer instructions. (SWS)

The Main Problems With the Viral Version

It can produce dangerously hot water

The source project reports outlet temperatures of 150°F or higher. CPSC warns that most adults can suffer third-degree burns after approximately two seconds of exposure to 150°F water. Even 120°F water can cause serious burns after prolonged exposure. (Practical Survivalist)

Never place your hand directly under the first water leaving a sun-heated collector.

Collect it in a bucket, mix it thoroughly, and measure it with a thermometer.

A small collector holds very little water

Approximately 20 feet of nominal half-inch Type L copper tubing holds only about 0.24 gallon, or 0.92 liter, of water.

That small quantity can become extremely hot when it remains stationary. But once it drains, cooler incoming water replaces it.

This creates an important tradeoff:

Very slow or stopped flow can produce a small amount of very hot water.
Faster flow produces more water, but at a lower temperature.
Continuous “super-hot” output requires much more collector area, storage, and control than the viral image suggests.

A direct garden-hose connection can pressurize the collector

Do not connect an improvised glazed collector directly to a pressurized household hose bib.

Municipal pressure, heated trapped water, closed valves, weak joints, inappropriate adapters, and uncontrolled collector temperatures can create leaks or sudden releases of hot water.

A professionally installed pressurized system requires appropriately rated components, relief protection, temperature control, and code compliance. The homemade version below instead uses a small vented gravity tank.

Not every plumbing part is suitable for hot potable water

Copper pipe, valves, adapters, solder, flux, sealants, hoses, and fittings should be documented for the intended water contact, temperature, and pressure.

For plumbing that provides water for drinking or other human-consumption uses, EPA requires lead-free pipes, fittings, fixtures, solder, and flux. “Lead free” generally means a maximum weighted average of 0.25% lead across wetted pipe and fixture surfaces and no more than 0.2% lead in solder and flux. (US EPA)

Do not use electrical solder or unknown recycled plumbing parts.

Materials

The original source uses a plywood collector approximately 23 by 35 inches with about 20 feet of half-inch copper tubing. The dimensions below produce a similar demonstration unit while incorporating safer connections and an open water path. (Practical Survivalist)

Copper absorber

Approximately 20 feet of half-inch Type L copper tubing
Lead-free copper elbows
Lead-free potable-water-rated solder
Potable-water-rated flux
Copper tube straps
Two potable-water-rated copper adapters
Copper tubing cutter
Deburring tool or round file

Use new copper intended for plumbing service.

Do not use tubing recovered from:

Refrigeration systems
Automotive equipment
Industrial machinery
Unknown construction debris
Plumbing that contained chemicals

Collector enclosure

One exterior-grade plywood back panel, approximately 24 by 36 inches
1×4 or 2×2 lumber for the perimeter
Exterior screws
Waterproof wood glue
High-temperature insulation
Thin aluminum or copper absorber sheet, optional
Exterior weather-resistant finish
Heat-resistant black coating
High-temperature sealant
Drain openings at the lowest corners

Mineral-wool insulation is suitable behind the absorber when it is protected from water and loose fibers cannot enter the plumbing.

Do not place exposed foam insulation directly against hot copper unless the product manufacturer specifically permits the expected temperature.

Transparent cover

Choose one:

Tempered glass
Reclaimed tempered storm-window glass in sound condition
Clear polycarbonate specifically rated for outdoor heat and solar applications

The glazing should be securely framed rather than resting loosely on small wooden dowels.

Tempered glass is designed to break into smaller fragments rather than large sharp shards, but it still requires careful handling and protective framing. (U.S. Consumer Product Safety Commission)

Gravity-water system

One vented food-grade supply container
One vented food-grade receiving container
Potable-water-rated flexible hoses
Potable-water-rated bulkhead fittings
One flow-control valve at the supply container
Open collector outlet with no downstream shutoff
Instant-read thermometer
Mixing bucket
Nonslip mat
Collector drain fitting, optional

The supply container should hold approximately three to five gallons for initial testing.

A small tank limits the amount of weight that must be elevated and makes the collector easier to supervise.

Structural support

Ground-mounted wooden or metal frame
Two rear braces
Wide feet
Ground stakes or sandbags
Hinges for tilt adjustment, optional

Do not install this homemade collector on a roof.

DOE guidance notes that solar-water collectors should be correctly oriented and securely mounted, and that roof installations must avoid structural damage and water intrusion. Certified systems should be installed in accordance with local building and plumbing codes. (Building Science Education)

Tools

Tape measure
Carpenter’s square
Pencil
Saw
Drill
Screwdriver
Copper tubing cutter
Propane plumbing torch
Heat-resistant mat
Clamps
Adjustable wrench
Safety glasses
Work gloves
Heat-resistant gloves
Fire extinguisher

Complete soldering outdoors or in an appropriately ventilated work area clear of combustible material.

Step 1: Choose the Collector Location

Select a level outdoor area receiving several hours of direct sunlight.

The site should be:

Away from children and pets
Away from walkways
Away from dry vegetation
Away from windows that could be damaged by reflected light
Close enough to inspect frequently
Protected from vehicles and lawn equipment
Suitable for water drainage
Free of overhead hazards

In the Northern Hemisphere, a generally south-facing orientation provides good solar exposure, although the best direction and tilt vary with location, season, shading, and intended use. (Building Science Education)

A ground-mounted stand is easier to inspect, drain, shade, and repair than a roof-mounted collector.

Step 2: Build the Wooden Enclosure

Cut a plywood back panel approximately 24 by 36 inches.

Build a shallow perimeter frame around it using 1×4 lumber.

The completed box should be deep enough to contain:

Insulation
Absorber panel
Copper tubing
A small air space
Transparent glazing

Attach the frame using waterproof glue and exterior screws.

Drill small drainage and ventilation openings near the lowest corners. These openings allow incidental condensation or rain intrusion to escape.

Do not make the collector airtight.

Although the glazing should reduce airflow, the wooden enclosure needs a way to release moisture that enters around seams.

Step 3: Add the Rear Insulation

Cut high-temperature insulation to fit the enclosure.

Install it against the plywood back.

Cover it with a thin metal absorber sheet or another suitable barrier. The barrier:

Protects the insulation
Gives the copper a stable mounting surface
Helps spread heat
Makes cleaning easier

Seal only the collector’s exterior wood joints. Do not coat copper joints or water-contact components with ordinary construction adhesive.

Step 4: Plan the Copper Layout

Lay the copper tubing and elbows on a flat work surface before cutting.

A practical layout uses several horizontal copper runs connected alternately at the left and right ends, creating a serpentine path.

Place:

The cold-water inlet at the lowest corner
The warm-water outlet at the opposite upper corner

This orientation helps air escape and allows the collector to drain more completely.

Keep the horizontal runs evenly spaced.

Avoid creating:

High loops trapping air
Low pockets trapping water
Tight elbow clusters
Sections impossible to reach for repair
Copper touching the future glazing

The source design places the copper extremely close to the glass. A small air gap is useful, but the pipe should not touch the glazing because expansion, vibration, or frame movement can damage it. (Practical Survivalist)

Step 5: Cut and Deburr the Copper

Measure every section before cutting.

Use a tubing cutter rather than a saw whenever possible.

After each cut:

Remove the internal burr.
Clean the outer surface.
Inspect the tube for deformation.
Dry-fit the elbow.
Mark its orientation.

Internal burrs can restrict flow and collect debris.

Do not leave copper shavings inside the completed collector.

Step 6: Solder the Serpentine Assembly

Assemble the copper circuit on a noncombustible surface.

For each joint:

Clean the pipe end and fitting.
Apply potable-water-rated flux sparingly.
Fit the pieces together.
Heat the fitting evenly.
Apply lead-free plumbing solder.
Allow it to cool naturally.
Wipe away excess flux.

Do not overheat the joint.

Do not perform torch work after the copper has been installed against plywood, insulation, painted surfaces, or other combustible material.

EPA requires lead-free solder and flux in plumbing supplying water for human consumption. Verify certification marks rather than assuming all plumbing products are equivalent. (US EPA)

Step 7: Conduct a Cold-Water Leak Test

Before mounting or painting the copper, connect the lower inlet to the vented supply tank.

Place the upper outlet over a bucket.

Open the supply valve slowly.

Let water fill the complete assembly and flow freely from the outlet.

Inspect every joint for:

Drips
Moisture
Misaligned fittings
Restricted flow
Trapped air
Water remaining after draining

Do not use compressed air to test a homemade assembly. Stored pneumatic energy can release suddenly when a fitting fails.

A gravity-water test is sufficient for this unpressurized demonstration collector.

Repair leaking joints only after draining and drying the assembly completely.

Step 8: Mount the Copper to the Absorber

Place the leak-free copper circuit inside the collector box.

Secure it using copper-compatible tube straps.

The fasteners should:

Hold the pipe firmly
Allow slight thermal expansion
Avoid flattening the tubing
Keep copper away from sharp screw points
Prevent contact with the glass

Where a metal absorber sheet is used, good physical contact between the copper and sheet helps heat transfer.

Do not rely on adhesive tape as the main pipe attachment.

Step 9: Apply the Black Absorber Finish

Clean grease and flux residue from the outside of the copper.

Apply a thin heat-resistant matte-black coating to the copper and absorber panel, following the coating manufacturer’s surface-preparation and curing instructions.

The coating belongs only on external collector surfaces.

Do not allow paint inside:

Copper tubes
Fittings
Hose connections
Valves
Water containers

Allow the finish to cure fully before installing the glazing or flowing water intended for washing.

A strong chemical odor indicates that additional curing and ventilation are needed.

Step 10: Install the Glazing

Build a removable frame around the tempered glass or rated polycarbonate.

Install a heat-resistant gasket or glazing tape around the collector perimeter.

Attach the cover using:

Hinges and latches
Removable screws with broad washers
Purpose-built glazing clips

The cover should:

Remain securely attached in wind
Avoid direct contact with copper
Allow access for repairs
Shed rain
Avoid placing concentrated pressure on the glass
Include enough clearance for thermal expansion

Do not permanently glue an unidentified glass sheet onto a wooden frame.

A removable cover makes inspection, repainting, leak repair, and winter storage much easier.

Step 11: Build the Ground Stand

Construct a broad triangular stand that tilts the collector toward the sun.

Include:

Two wide feet
Two rear braces
A crossbar
Ground anchors or sandbags
A stop preventing the panel from falling flat
An optional hinge for angle adjustment

Test the empty structure before connecting water.

Push gently from each direction.

The collector should not rock, twist, or threaten to fall.

Remember that copper, glass, framing, and water add considerable weight.

Step 12: Position the Supply Tank

Place the vented supply container on a sturdy platform slightly above the collector inlet.

The container must never be supported by:

A loose chair
Stacked buckets
A folding table
Unsecured concrete blocks
A ladder
The collector itself

Install a potable-water-rated outlet and supply valve near the bottom.

Connect it to the collector’s lower inlet.

Keep the supply container vent open while water is flowing.

The vent allows air to replace departing water and prevents the flexible tank or plumbing from being drawn into a vacuum.

Step 13: Keep the Outlet Open

Connect a short potable-water-rated hose to the collector’s upper outlet.

Route it downward into a vented receiving container.

There must be:

No shutoff valve at the collector outlet
No kink in the hose
No cap
No submerged tube end
No sealed receiving vessel

Water must be free to leave the sun-heated collector at all times.

A valve may control water entering from the supply tank, but the collector must never be trapped full of water between closed valves.

When flow is stopped, shade or drain the collector.

Step 14: Perform the First Solar Test

Choose a mild sunny day.

Fill the supply tank with clean cold water.

Record the starting temperature.

Open the supply valve until a slow stream enters the collector. Allow the system to fill completely and begin flowing from the outlet.

Then reduce the flow gradually.

Collect outlet water in a bucket and measure:

Temperature after 15 minutes
Temperature after 30 minutes
Temperature after one hour
Volume collected
Outdoor temperature
Cloud cover
Approximate flow rate

Do not touch the copper, glazing, or first outlet water directly.

The first commissioning water should be discarded because the collector may still contain residue from new copper, flux, soldering, paint curing, hoses, or sealants.

How to Adjust the Water Temperature

The flow rate controls the result.

Slower flow

Water remains inside the collector longer and generally exits warmer.

Risks include:

Scalding temperatures
Low total output
Greater stagnation
More scale formation
Larger temperature changes during passing clouds

Faster flow

Water exits cooler, but the system produces more total volume.

Stopped flow

Water trapped inside the sunny collector may become extremely hot.

Do not intentionally leave a full collector sitting in the sun with no open circulation path.

Shade the collector or drain it when water is not moving.

Realistic Performance

The source article reports temperatures of 150°F or higher during relatively cool outdoor conditions. A glazed black copper collector can indeed become much hotter than the surrounding air under strong sunlight, particularly when water remains stationary. That result does not mean the collector can continuously deliver a large flow of 150°F water. (Practical Survivalist)

Actual output depends on:

Collector area
Sun intensity
Outdoor temperature
Wind
Glazing
Insulation
Copper-to-absorber contact
Starting water temperature
Flow rate
Collector orientation
Shade
Internal scale

A small collector can produce:

A little very hot water after stagnation
A slow stream of warm water
A faster stream with only modest temperature gain

It cannot provide unlimited hot water.

Certified collector ratings exist so systems can be compared under standardized test conditions. Homemade collectors have no independently verified output, pressure rating, durability rating, or stagnation-temperature limit. (Solar Rating)

Measure your own system instead of promising a particular temperature or gallon-per-hour figure.

Preventing Scalds

Treat all water leaving the collector as potentially dangerous.

CPSC reports that 150°F water can cause third-degree burns in approximately two seconds, 140°F water in approximately six seconds, and 130°F water in about 30 seconds. CPSC recommends 120°F as a residential water-heater setting intended to reduce most tap-water scald injuries, although prolonged contact at 120°F can still cause burns. (U.S. Consumer Product Safety Commission)

Before using the water:

Collect it in an open container.
Mix the entire volume.
Measure it with a thermometer.
Add cold water.
Mix again.
Recheck the temperature.
Test cautiously before washing.

Never allow children, older adults, or anyone with reduced temperature sensation to operate the collector unsupervised.

Do not connect the outlet directly to a showerhead without a properly designed mixing and anti-scald arrangement.

Do Not Connect It to Household Plumbing

A homemade collector should not be inserted directly into:

A water heater’s supply line
A pressurized shower line
A kitchen faucet
A washing-machine connection
A domestic hot-water recirculation loop
A municipal water line

A permanent residential system requires a qualified design that addresses:

Local plumbing and building codes
Collector certification
Complete-system certification
Pressure ratings
Temperature-and-pressure relief
Thermal expansion
Backflow protection
Potable-water materials
Freeze protection
Overheating
Tempering valves
Structural mounting
Roof penetrations
Drainage
Electrical controls when pumps are used

NREL specifications call for code-compliant freeze protection, suitable piping, isolation valves, drain arrangements, and a temperature-and-pressure relief valve on solar water-heating installations. (SWS)

A plumber or qualified solar-thermal installer should handle any connection to a home’s permanent water system.

Warm-Water Stagnation and Legionella

Warm stagnant water can support biofilm and bacterial growth.

CDC identifies water temperatures of approximately 77°F to 113°F as favorable for Legionella growth. Slow or absent water movement, scale, sediment, reduced disinfectant, and biofilm can increase risk. Showers can aerosolize contaminated water into droplets that may be inhaled. (CDC)

To reduce stagnation:

Drain the collector after every use.
Do not leave warm water inside for days.
Flush the system before use.
Eliminate low points that retain water.
Clean the supply and receiving tanks.
Inspect tubing for slime or odor.
Store the collector dry when possible.
Clean hoses and showerheads regularly.
Avoid using stagnant collector water for drinking.

People at increased risk of severe Legionnaires’ disease—including older adults, smokers, people with chronic lung disease, and those with weakened immune systems—should be particularly cautious with homemade systems that generate warm aerosolized water. (CDC)

Can You Drink the Heated Water?

This homemade collector is best designated for external washing and utility use.

Using it for drinking water introduces additional concerns:

Materials may not be certified for potable hot water.
Flux or solder residue may remain.
Warm stagnant water can support biofilm.
Water may remain in difficult-to-clean sections.
Copper leaching depends partly on water chemistry.
The collector has no sanitation control.
The storage containers may become contaminated outdoors.

When potable use is intended, every wetted component should be certified for drinking-water contact and its stated maximum operating temperature. A professionally designed or independently certified system is the more reliable option. EPA guidance also recommends using cold tap water—not warm or hot plumbing water—for drinking and cooking because hot water can contain higher levels of metals leached from plumbing. (US EPA)

Do not drink directly from this collector.

Freeze Protection

Water expands when it freezes and can rupture copper tubing, joints, valves, and fittings.

Direct solar-water systems carrying ordinary water through outdoor collectors are vulnerable in freezing climates. DOE and NREL guidance calls for appropriate freeze protection, including approved indirect glycol loops, drain-back systems, supplemental heat, or other code-compliant methods. (SWS)

For this simple project:

Close the supply valve.
Open the collector outlet fully.
Disconnect the lower inlet.
Tilt the panel toward the drain.
Allow all water to leave.
Blow only with lung pressure when needed—never compressed air.
Store hoses and valves indoors.
Move the collector under shelter before freezing weather.

Because serpentine tubing can retain water in low points, “mostly drained” may not be sufficient.

Use unions or removable fittings that allow the panel to be rotated and drained completely.

Overheating Protection

A glazed collector can continue heating when no water is needed.

Prevent excessive temperatures by:

Draining the collector
Covering it with an opaque reflective panel
Turning it away from the sun
Increasing water flow
Removing the glazing during seasonal storage
Using a removable shade cloth
Operating it only while supervised

Do not throw cold water onto extremely hot glass.

Sudden temperature change may damage the glazing.

Do not cover a hot collector with plastic sheeting or another material that could melt.

Use a rigid light-colored cover that can be installed without touching the hot glazing.

Weather and Wind Protection

The glass panel turns the collector into a broad surface that can catch strong wind.

Bring the unit under shelter before:

Severe thunderstorms
High-wind warnings
Hail
Tropical storms
Freezing rain
Heavy snow

Inspect it after every significant weather event.

Look for:

Cracked glazing
Loose screws
Failed sealant
Warped wood
Displaced copper straps
Water inside the enclosure
Damaged hoses
Corroded fittings

Do not operate a collector with cracked glass or a shifting frame.

Cleaning and Maintenance

After each use

Drain the copper tubing.
Empty both water containers.
Flush the collector.
Check the outlet for unrestricted flow.
Dry the hoses.
Inspect for leaks.
Shade or cover the panel.

Monthly during regular operation

Wash the glazing.
Inspect the black absorber coating.
Check copper straps.
Inspect solder joints.
Clean the containers.
Check hoses for softening or cracking.
Inspect the frame and stand.
Confirm the thermometer is working.

At the end of the season

Flush the collector.
Drain it completely.
Remove flexible hoses.
Open the glazing.
Inspect for scale and corrosion.
Repair damaged paint.
Dry the enclosure.
Store the panel protected from weather.

Mineral scale inside the tubing can reduce flow and heat transfer.

Use only a cleaning method compatible with copper and rinse until no residue remains.

Common Building Mistakes

Connecting directly to a hose bib

Household water pressure turns the collector into a pressurized hot-water device.

Use a vented gravity tank instead.

Installing valves at both ends

A water-filled collector must not be trapped between closed valves while heated.

Keep the outlet open.

Using leaded solder

Use certified lead-free plumbing solder and flux for any water-contact system. (US EPA)

Installing unidentified PVC adapters

Plastic components must be specifically rated for the water temperature and pressure they may experience.

Do not assume a cold-water garden fitting is suitable for 150°F water.

Letting copper touch the glass

Expansion or frame movement may damage the glazing.

Maintain clearance.

Supporting glass with thin loose dowels

Use a proper perimeter glazing frame designed to distribute the load.

Leaving air trapped in the collector

Install the inlet low and the outlet high.

Avoid high loops.

Expecting continuous 150°F output

The hottest result may be only the small volume that remained stationary inside the tubing.

Measure both temperature and collected volume.

Using the water without mixing

The first outlet water may be dangerously hot.

Collect, mix, and measure it.

Leaving water stagnant

Warm stationary water encourages biofilm and can enter the temperature range favorable to Legionella. (CDC)

Failing to drain before frost

Even a small quantity of trapped water can damage the tubing.

Mounting the collector on a roof

A homemade roof installation adds fall, structural, wind, leak, and plumbing hazards.

Keep this project on the ground.

Optional Improvements

Add a metal absorber plate

Mount the copper tightly against a black aluminum or copper sheet.

The sheet spreads solar heat across a larger surface and may improve transfer into the tubing.

Add a flow meter

A small low-pressure flow meter helps compare temperature rise against water volume.

Add inlet and outlet thermometers

Use two probe thermometers to measure:

Incoming water temperature
Outlet temperature

This gives a much clearer picture of collector performance.

Add an insulated receiving container

A vented insulated container helps retain the collected heat.

It must remain open to atmospheric pressure and should never be tightly sealed while receiving hot water.

Add a removable reflector

A flat side reflector can direct additional sunlight toward the collector.

Position it carefully so it cannot concentrate light onto wood, people, vehicles, windows, or neighboring property.

Build two smaller panels

Two portable panels may be easier to handle than one large heavy collector.

Connect them only through an open, unpressurized arrangement.

Upgrade to a certified system

For permanent household hot water, consider an ICC-SRCC-certified collector and complete solar-water-heating system. OG-100 certification evaluates individual solar collectors, while OG-300 evaluates the broader system design and components. (Solar Rating)

Is This Project Worth Building?

Yes—when it is presented honestly as a small solar water preheater.

Its strengths include:

No electricity during operation
Simple visible operating principle
Reusable copper construction
Useful warm water in sunny weather
Adjustable flow
Educational value
Potential reduction in later heating energy

Its limitations include:

Very small internal water volume
Weather-dependent output
Serious scalding potential
No automatic temperature control
Freeze vulnerability
Stagnation and hygiene concerns
No pressure rating
No certified performance
Need for continuous supervision

Build it before an emergency.

Start with a small supply tank.

Measure the temperature and volume.

Practice mixing the water safely.

Drain the panel after every test.

A modest open system that you understand is far more useful than a pressurized “super-hot” collector copied from an image without temperature or pressure control.

Final Safety Note

This project is an unpressurized, ground-mounted solar water preheater.

Do not connect it directly to municipal water, household plumbing, a pressurized storage tank, or a closed shower system. Never trap water between closed valves while the collector is exposed to sunlight.

Use certified lead-free plumbing materials and components rated for the expected temperature. Treat all outlet water as potentially scalding. Collect it in an open container, mix it with cool water, and verify the temperature before use.

Drain and flush the collector after use. Protect it from freezing, stagnation, high wind, and overheating. A permanent domestic solar-water system should be selected and installed by qualified professionals in accordance with local codes.