Water and salt lamps that last 45 days? We investigate if it is possible, what voltage they generate and what the viral video hides

On July 26, 2026, the user @sebastia_me viralized a clip on X with a striking statement: water and salt lamps are chemical batteries whose electrolyte It is salt water between two metals, and a single glass of seawater can generate up to 45 days of continuous lightwithout sun or plugs. The video is not his: it is a republished from Interesting World (@_fluxfeeds), originally published on December 4, 2025, where an emergency LED lamp is seen turning on when salt and water are added. We investigate the viral clip, the Colombian WaterLight project (where the 45-day figure comes from), the real chemistry, and we separate verifiable science from embellished marketing.

What exactly does the viral video show

The post by @sebastia_me links to the video by Interesting World (@_fluxfeeds). In the clip you can see a tubular emergency flashlight - the type sold as a "salt water lamp" or "water activated lamp" - to which water and a sachet of salt are added; When the circuit is closed, the LED lights up. The author's original English text is short: «DIY salt-water battery lighting up an LED».

The Spanish text added by @sebastia_me generalizes the chemistry (essentially correct) and mixes the promise of “45 days of continuous light with a glass of sea water”, which corresponds above all to the marketing of another product: WaterLight, the Colombian lamp from E-Dina. They are two related but different things:

• The viral video: demonstrates the principle—galvanic cell with saline electrolyte—in a commercial or homemade emergency lamp.
• WaterLight: 2021 humanitarian project with Wayúu design, 500 ml of sea water and the figure of 45 days promoted by the company.

The first half of the tweet is essentially correct: it is a chemical battery with a saline electrolyte between two metals. The second half—“a glass of seawater = 45 days of continuous light”—applies mostly to WaterLight, not necessarily to the device in the Interesting World clip.

WaterLight: where does the 45 day figure come from

WaterLight is a portable flashlight developed by the Colombian startup E-Dina together with Wunderman Thompson, presented in 2021 for coastal communities without an electrical grid —especially the indigenous Wayúu people, in La Guajira. According to Dezeen and Interesting Engineering:

• 500 milliliters of seawater (or, in an emergency, saline urine) are poured into the wooden cylinder.
• The company promises up to 45 days of lighting per electrolyte recharge.
• Total useful life: about 5,600 hours (2–3 years of intermittent use).
• Includes USB port to charge phones at low power.

Is it possible? Yes: chemistry has been working for a century

Saltwater lamps are not alchemy or free ocean energy. They are metal-air batteries (also called galvanic cells or, in some cases, metal fuel cells), a family of electrochemical devices in commercial production for almost 100 years. If you know the button batteries that hearing aids use, you've already had one in your hand: many are zinc-air.

The mechanism, rigorously explained by chemical engineer Joey D. Ocon in Rappler when analyzing the Philippine SALt lamp (another viral product of 2015), is this:

1. Metal anode: a highly oxidizable metal (magnesium, aluminum or zinc) gives up electrons when oxidized.
2. Air cathode: atmospheric oxygen is reduced on a porous plate with a catalyst (manganese, cobalt or, in the laboratory, platinum).
3. Aqueous electrolyte: the saline solution (NaCl in water) allows the ions to move between both poles. Closing the circuit with salt water is equivalent to “turning on the switch”, as Ocon describes.
4. Electric current: Electrons flow through the external circuit to the LED or USB port.

The overall reaction in a magnesium-air cell with neutral electrolyte can be summarized as follows:

2 Mg + O₂ + 2 H₂O → 2 Mg(OH)₂

Metallic magnesium disappears; Oxygen from the air is the other essential reagent. Salt water does not provide energy: it only facilitates ionic transport. Any electrolyte with enough ions would do—even a basic potassium hydroxide solution would give better performance, although it is more corrosive and difficult to handle.

What voltage and power they generate

Here is the direct answer to the viral comment's question ("what tension do they generate?"):

Cell type	Open circuit voltage (approx.)	Notes
Magnesium-air	1.5–1.6 V	Used in WaterLight and commercial Mg-air emergency lamps
Zinc-air	1.4–1.65 V	Hearing aid batteries; SALt (Philippines) used zinc with a lifting circuit
Aluminum-air	1.2–2.0 V	High energy density; rapid corrosion in salt water
Mg/Al-air commercial lamps	3–4.5 V (after booster)	Joule thief circuit or several cells in series to power white LEDs

A low-power white LED typically needs 2.8–3.2 V and about 10–30 mA for modest brightness. That is equivalent to 0.03–0.1 W. Magnesium-air emergency lamps on the market declare between 0.5 W and 1 W nominal power and voltages of 4.5 V after the booster circuit—enough to illuminate a small room or charge a cell phone very slowly via USB.

WaterLight does not publish a detailed data sheet with exact voltage, but Dezeen confirms that the ionization process between magnesium and copper plates produces a continuous current of low voltagethat powers the integrated LED and the USB port. The official website (waterlight.com.co) mentions "aluminum" in a section and "magnesium" in the video: the internal design has probably evolved, but the principle is the same.

How long does it really last? The 45 days explained

The figure of 45 days does not come out of the air, but it must be read with a magnifying glass:

• E-Dina and its partners claim that half a liter of salt water provides up to 45 days of electricity. They do not always specify whether it is continuous light 24/7 or intermittent night use.
• The total useful life of the device is around 5,600 hours. If we divide: 5,600 ÷ 45 ≈ 124 "cycles" of electrolyte... but each cycle also consumes part of the internal metal. The real limit is not just the water: it is the metal anode that dissolves.
• The SALt lamp from the Philippines, reviewed in Inquirer, promised 8 hours a day for 6 months with proper maintenance, replacing the metal anode every six months. That's ~1,440 hours per metal cartridge — consistent with the order of magnitude.
• Chinese emergency Mg-air lamps declare ≥120 continuous hours (5 days) with 300 ml of brine and 0.5 W — verifiable industrial catalog data.

Doing the numbers with a 0.05 W (50 mW) LED:

• 45 days × 24 h = 1,080 continuous hours → energy ≈ 54 Wh.
• A small commercial magnesium cartridge can store on the order of 50–100 Wh theoretically, but actual efficiency (parasitic corrosion, polarization, H₂ leakage) reduces performance to 50–70%.
• Conclusion: 45 days is plausible only with very dim LED or intermittent use, not with a powerful bulb on day and night. Marketing rounds up; physics imposes a ceiling.

Editorial note: we have not replicated the 45 days of WaterLight in the laboratory; The autonomy figures come from the company and from media such as Fast Company and Dezeen, contrasted with the state of the art in metal-air batteries.

What you need to build one (and why it's not "just water and salt")

If you would like to replicate the principle in a workshop, these are the essential components:

Component	Function	It is consumed
Metal anode (Mg, Al or Zn)	Real source of electrons; rusts	Yes — it must be replaced
Air cathode (grid + MnO₂ catalyst)	Reduces atmospheric O₂	It degrades over the years
Electrolyte (water + salt, ~3–5% NaCl)	Conducts ions; close the circuit	It is depleted/polluted; is renewed
Porous separator	Avoid short circuit between anode and cathode	No
Booster circuit (joule thief / boost)	Go up 1.5 V to 3+ V for the LED	Reusable electronics
LED + resistor	Emits light	LED lasts for years; metal does not
Gas valve	Releases H₂ generated in corrosion	WaterLight includes it (perforated lid)

A home science experiment with zinc nail + copper coin + lemon or brine produces about 0.8–1.0 V and barely lights up an LED without a booster. To get close to WaterLight requires air electrode engineering, corrosion control, and a design that manages hydrogen — hence the commercial product is not “a glass and two spoons,” but a patented cartridge.

What the video doesn't tell (and marketing omits)

After reviewing the Interesting World clip, the official WaterLight video, and Rappler's analysis of SALt, these are the biggest blind spots:

• Metal is the fuel. Without a new magnesium or aluminum cartridge, seawater does not ignite anything. It's like saying that gasoline works "only with air": the air participates, but the fuel is another.
• Corrosion even off. If you leave the electrolyte in, the metal continues to dissolve and release hydrogen. The brine must be emptied when not in use (SALt and Chinese manufacturers warn this).
• Modest performance. It does not replace a 20 W solar panel or a generator. It is used as an emergency light, night fishing or charging a mobile phone with patience.
• Supply chain. Ocon noted in Rappler that distributing metal anodes to remote communities is as complex as distributing batteries or kerosene.
• Patents and copies. The base technology is in the public domain; The value is in the air electrode design and integration. WaterLight patented its prolonged ionization method, according to Colombian media.
• Limited commercial availability. WaterLight was presented as a social prototype for La Guajira; It is not a shelf product on Amazon in the style of generic Mg-aire flashlights (~15 USD, 120 hours).

Three products, one chemistry: viral, WaterLight and SALt

	Viral clip (Interesting World)	WaterLight (Colombia, 2021)	SALt (Philippines, 2015)
What is it	Demo video with generic Mg/Al-air lamp	Wayúu + E-Dina humanitarian project	Filipino startup (APEC 2015, Obama)
Metal	Internal metal cartridge (emergency type)	Magnesium (video) / aluminum (web)	Zinc + booster circuit
Electrolyte	Water + sachet of salt	500 ml sea water	1 tablespoon salt + 1 glass water
Declared autonomy	Similar catalogs: 120–180 continuous hours	Up to 45 days / 5,600 total hours	8 h/day × 6 months; anode every 6 months
Status	Viral clip reposted in 2026	Social pilot / prototype	Massive coverage; limited production

All three cases share the same simplified media narrative: “lamp that runs on salt water.” Electrochemical Engineers (Rappler, Inquirer) clarified that calling them “saltwater lamps” without mentioning the metal is scientifically irresponsible, although it does not imply deliberate fraud.

How we research this article

1. We identify the original video from the republished from @sebastia_me to @_fluxfeeds.
2. We download the X clip and contrast it with the official presentation of WaterLight on YouTube.
3. We review technical and informative documentation: Rappler (SALT analysis), Dezeen, Interesting Engineering and literature on Mg-air batteries (MDPI).
4. We calculate orders of magnitude of energy (Wh) to evaluate whether “45 continuous days” fits the physics.

Limit: We do not manufacture or test a prototype in our facilities; the verdict is based on documentary evidence and established electrochemical principles.

Does the viral tweet lie?

We rate each statement:

Affirmation	Verdict
«They are chemical batteries with salt water electrolyte between two metals»	True
«A glass of sea water generates energy»	Deceptive — the water closes the circuit; energy comes from metal that oxidizes
«Up to 45 days of continuous light»	Partially true — company figure, conditional on low-consumption LEDs and specific design; It is not universal
«Without sun or plugs»	True — real advantage over solar in cloudy or interior areas
Implicit: free and infinite energy of the sea	False — metal must be replaced and electrodes maintained

Final verdict

Yes, it is possible. Salt-water lamps work because metal-air electrochemistry is one of the oldest and most efficient (in energy density by weight) ways to generate portable electricity. The viral video of Interesting World, republished by @sebastia_me, shows the principle in a real emergency lamp; WaterLight is the project that brings that idea to coastal communities with the promise of 45 days.

But it's not sea magic. They generate between 1.5 V and 4.5 V depending on their design, they consume magnesium, aluminum or zinc that must be replaced, and the "45 days" are an optimistic commercial promise linked above all to WaterLight, not a law of physics applicable to any lamp on the clip. Everyday chemistry can light up a room; The invisible fuel is not salt, but metal that, little by little, turns into light.