The solar still is the oldest water purifier there is — evaporate under glass, condense on the glass, collect the drops — and the modern build turns that campfire physics into a working backyard appliance: a glazed basin still that produces genuinely distilled water from rain, pond, or questionable sources, every sunny day, on nothing. It's the dehydrator and air heater builds' sibling in the passive-solar family, the preparedness catalog's quietest member, and an honest chemistry lesson in plywood. Here's the build, the yield math, and what distilled water is actually for.
How a basin still works
The machine is a sealed greenhouse with a slope: a shallow blackened basin holds the source water; glazing above it traps solar heat until the water evaporates; the vapor — leaving salts, sediment, metals, and biology behind in the basin — condenses on the cooler underside of the tilted glass and runs down its slope into a collection trough, out a tube, into your jug. Purity is the physics' gift: distillation is the separation method everything else imitates, and what condenses is water alone (with the honest caveat that volatile compounds can travel with the vapor — the reason stills feed on rain, pond, and brackish sources rather than fuel-contaminated ones). Yield is the physics' price: evaporation is energy-hungry, so output measures in quarts-per-sunny-day per basin, not gallons-per-hour — the still is a drinking-water machine, not a household supply, and every design choice below serves squeezing more drops from the same sun.
Component list
Glazing: tempered glass panel
$The condenser: single-pane tempered glass at the classic shallow tilt — steep enough that drops run to the trough instead of falling back, shallow enough to face the sun. Glass beats polycarbonate here specifically: condensation sheets on glass and beads on plastics, and sheeting is yield. The salvaged-door trick from the oven build applies.
Basin: food-safe black liner or coated pan
$The evaporator: a shallow basin — wide beats deep; surface area is the throughput — in food-safe black form: an EPDM pond liner rated potable, a purpose blackened metal pan, or high-temp black coating certified for contact. The food-safe line from the dehydrator build governs absolutely: everything the water or vapor touches must be rated for it.
Insulated box & sealing
$The retention body: the air heater build's double-walled, foam-insulated construction under and around the basin, with high-temp sealing at the glazing — every leaked degree is unevaporated water. The trio of passive builds (heater, dehydrator, still) share this carpentry so completely that veterans batch them.
Collection: trough, tubing & jug
$The harvest path: a food-grade trough (PVC channel or formed metal) at the glass's low edge, silicone or food-safe tubing through a sealed pass-through, and a covered collection jug shaded against re-warming. Slope discipline throughout — drops obey gravity exactly, and a level trough is a puddle, not a spout.
Feed & flush plumbing
$The service side: a fill port for the morning charge, a basin drain valve for the flush that carries off the concentrated leavings (the still's one chore — brines and sediment concentrate by design and leave by valve), and a float-fill upgrade from the irrigation build's parts for the set-and-forget tier.
Instrumentation & the mineral question
$The finishing pair: a thermometer in the basin airspace (the passive family's craft-versus-hope rule, third appearance) and — for households drinking the output daily — remineralization drops or a mineral cartridge, since distilled water's purity includes the minerals' absence and taste-and-habit both have opinions. TDS meters make the purity claim a reading.
The build, in order
Carpentry per the passive family's shared pattern: insulated box, basin seated and sealed, glazing fitted at its tilt with the trough aligned under the low edge and proven with a squirt bottle before anything cures — the water test here is literal and pre-emptive. Food-safe cure time honored in full (the paint-and-liner off-gassing days outdoors, non-negotiable when the product is drinking water), pass-throughs sealed, jug shaded. Commission with the two-stage test: a plain-water run first, measuring the sunny-day yield that becomes your still's honest number, then — the persuasion ceremony — a salted or food-colored basin charge whose condensate comes out clear and neutral, with the TDS meter turning the magic trick into a data point. Site it like the oven: full sun, wind shelter, and the reflector-wing upgrade borrowed wholesale where ambition strikes.
Feed water strategy: what goes in the basin
The still's menu, ranked by fit. Rainwater is the ideal feed — low mineral load, minimal flushing, and the barrels already collect it, which is why the still-plus-barrels pairing anchors the preparedness mission. Pond and creek water follow with a pre-filter courtesy (a cloth or sediment screen at the fill port keeps the basin's flush chore civilized) and the still's biology-defeating physics doing the real work. Brackish and salty sources work by design at the cost of an eager flush schedule. The declined list matters equally: fuel-, solvent-, or pesticide-contaminated water can send volatiles over with the vapor — the one contamination class distillation's magic trick doesn't cover — and greywater's soaps ride the same caution. Feed honestly, flush faithfully, and the physics handles the rest.
Yield math and honest missions
Output scales with basin area, sun, and sealing quality — quarts per sunny day per household-scale still — which sorts the missions honestly. Preparedness is the headline: a still in the shed converts the rain barrels' stored volume into drinking-grade water indefinitely, no filters to stockpile, no fuel to burn — the Blackout Box's water chapter, solved in plywood. Daily-use niches follow: distilled water for the CPAP humidifier (the medical guide's quiet consumable), steam irons, aquarium top-offs, and battery service — the household purchases the still simply retires. Off-grid and brackish-source missions scale by adding basins rather than chasing bigger ones. The counter-missions deserve equal honesty: the still doesn't out-produce a filter for volume, doesn't handle fuel-contaminated sources, and doesn't replace municipal water for a family's cooking-and-drinking total — it's the purity specialist in the water plan, not the plan.
Care, seasons, and the family of designs
The operating rhythm is the passive family's gentlest: morning fill, evening collect, and the periodic flush that drains the basin's concentrated leavings — plus a glazing wipe inside and out on the schedule the yield tells you (film on the glass is stolen condensation). Winter parallels the oven's: clear-cold days produce respectably while hazy-warm ones disappoint, and hard-freeze climates drain and rest the still or run it as the greenhouse's winter tenant. The design family branches like its siblings': the wick still (fabric wicks lifting water into the vapor path) trades simplicity for yield, the multi-basin cascade scales output, and the emergency tier — the pit still and the transpiration bag — belongs in the same preparedness notebook as the build itself, because the physics that runs the appliance also runs the improvisation. Skills-wise this is the passive trilogy's capstone: whoever has built the heater, the dehydrator, and the still owns the whole glazed-box craft — and drinks the proof.
Bottom line
A black basin, tilted glass, a trough that obeys gravity, and food-safe discipline throughout — quarts of genuinely distilled water per sunny day, from sources you wouldn't otherwise drink. Build it as the rain barrels' purifier, the CPAP's supplier, and the preparedness plan's quietest member; test it with the salt trick; and let the TDS meter make the oldest water purifier on earth show its work.
Frequently Asked Questions
How much water does a solar still actually produce?
Quarts per sunny day per household-scale basin — scaling with basin area, sun, and sealing quality. It's a drinking-water specialist, not a volume supply; the two-stage commissioning test gives your build its honest number.
Is solar-distilled water safe to drink?
Distillation leaves salts, sediment, metals, and biology behind in the basin — it's the purification method others imitate — with the caveat that volatile contaminants can travel with vapor, so stills feed on rain, pond, and brackish sources, never fuel-contaminated ones. Food-safe materials throughout are non-negotiable.
Why does my still produce less than expected?
The usual suspects in order: leaked seal (every escaped degree is unevaporated water), filmed glazing (stolen condensation), a too-deep basin (surface area is throughput), or a trough slope problem sending drops back to the basin. The thermometer and a squirt-bottle trough test find them fast.
Does distilled water taste flat?
It tastes like nothing — the minerals' absence is the purity — which suits appliances perfectly and drinking preferences variably. Remineralization drops or a mineral cartridge answer the taste question for daily drinkers.
Can the still work with salt water?
Yes — basin distillation handles brackish and salty sources by design; the salts stay behind and leave via the flush valve. It's the classic desalination physics at backyard scale, with the flush chore scaling alongside the source's salt.