Part IV: Solar Water HeatingChapter 6. Simple and Batch Water Heaters

Solar Camp and Garden Showers

Small unpressurized showers for a garden or campsite, with the burn and scald hazards called out.

Difficulty: Beginner
Cost: $20–80

published

A garden shower is a dark tank or bag of water, left in the sun, then lifted so gravity can push a few gallons through a shower head. It is not a domestic hot-water system. It is not pressurized, it is not a source of drinking water, and it can scald you on a clear afternoon just as surely as a household heater can.

Five gallons is enough for a short rinse. That water weighs a bit over 40 pounds. Twenty gallons weighs about 170 pounds. The stand, the branch, or the hook has to hold that load while someone is standing under it and tugging the hose. A stepladder is not a stand.

If you want hot water at a tap in the house, this is the wrong page. Use the batch heater only where it never freezes, or the system choice guide everywhere else.

Difficulty

Level: Beginner
Time: An afternoon to set up, and a temperature check every single use
Skills: Tying a load down and refusing to step under untested water

Cost estimate

$20–80

A commercial camp bag lands near the low end. A dark tank, a real valve, a thermometer, and lumber for a stand land near the high end. Do not spend the savings on a sealed cap.

Piece	Typical cost
Five-gallon camp bag or dark tank	$15–40
Valve, hose, and shower head	$10–25
Thermometer	$8–15
Lumber for a four-leg stand	$0–20

Materials

Item	Qty	Notes
Dark water container	5 gallons per person is plenty	A container sold for water. Not a fuel can, not a pesticide barrel, not a glass carboy.
Vent or loose lid	1	The tank stays open to the air. A sealed vessel in the sun becomes a pressure vessel.
Valve you can reach from outside the spray	1	Plus a way to add cold water. The shutoff must not require you to stand in the stream.
Thermometer	1	Read it every time. A hand waved through the stream is a late warning.
Stand	1	Four legs, on flat ground, able to hold the full tank plus a person bumping it. No ladders.

What the sun actually does

A black bag or a dark tank absorbs sunlight and warms the water inside. A clear or white container does less. Leaving the water out for a few hours on a bright day is the whole collector. There is no pump and no glazing required, though a simple clear cover on a tank will get you hotter, faster, and also closer to a burn.

The first water out of a dark hose that has been lying in the sun can be hotter than the tank. That hose is a second collector. Run it onto the ground, away from your feet, until the temperature stops climbing, then test again.

At a campsite, follow the site's rule for wash water. At home, keep soap out of a creek, a pond, and a storm drain. A mulched patch of ground is the usual place for a light rinse. If your town regulates graywater, this hose is still graywater.

The tank is open to the air and up on a stand that can hold it. The valve is where you can reach it before you step under the spray.

Heat, weight, and a cap you must not tighten

Water warmer than about 120 degrees F scalds, and a black container in full sun can go well past that. Children, older people, and anyone who cannot step aside quickly can be burned before they understand what happened. Mix cold water in first. Read the thermometer. Then get in.

If you cap the tank and leave it in the sun, the water expands and the pressure rises. Camp bags have split this way, and a metal tank with a tight lid can do worse. Fill it, leave a vent, and disconnect any hose that is still connected to a pressurized spigot. A garden faucet left attached to a closed tank in the sun can swell a harmless bag like a balloon.

Do not drink the water. A typical garden hose is not a drinking-water pipe, and water that sat warm all afternoon is wash water only. Dump what you do not use. Do not save a lukewarm tank for the next weekend.

Where nights freeze, drain the tank and the hose before dusk. A little ice will split a fitting, and a frozen hose full of water is a surprise the next sunny morning when the first slug comes out hot and then the ice lets go.

Set the volume and the stand
Plan on about five gallons per person. Build or buy a stand that will not tip when the tank is full. Put it where the site survey says you have sun, and where the runoff has somewhere legal to go.
Fill it open, then leave it
Fill from a hose, disconnect the hose, and leave a vent. Give the water a few hours of sun. Do not seal the lid to "hold the heat."
Run the hose onto the ground
The first water in a sun-baked hose can be the hottest. Discharge it away from people until the stream settles.
Mix, measure, then shower
Add cold water until a thermometer at the head reads a temperature you would accept from a house shower, near 100 to 105 degrees F for a rinse. Confirm the valve is reachable without standing under the spray.
Drain it when you are done
Empty the tank and the hose. At a camp, follow the site rule. At home, do not leave warm water sitting for days, and do not leave a full tank up on the stand overnight if children play there.

Difficulty

Cost estimate

Materials

What the sun actually does

Heat, weight, and a cap you must not tighten

Set the volume and the stand

Fill it open, then leave it

Run the hose onto the ground

Mix, measure, then shower

Drain it when you are done

Further reading