What you're looking at — quick overview

You listed a lot of related things: Mel Science kits (educational chemistry kits), electrolyzers and generators (for hypochlorous acid, sodium hypochlorite, or hydrogen), electrolysis (the underlying process), distilled water (from a countertop distiller), and uses like swimming pools or so-called "hydrogen water." Below I explain the chemistry and technology step by step in a way that makes sense for a 15‑year‑old, and I highlight safety and safer experiments you can do with kits or at school.

1. What is electrolysis?

Electrolysis is a way to use electricity to drive chemical reactions that normally don’t happen by themselves. In a simple water electrolysis setup, a pair of electrodes (a positive anode and a negative cathode) are placed in water and a voltage is applied.

• At the cathode (negative) water is reduced to produce hydrogen gas: 2 H2O + 2 e‑ → H2 + 2 OH‑
• At the anode (positive) water is oxidized to produce oxygen gas: 2 H2O → O2 + 4 H+ + 4 e‑
• Overall simplified reaction: 2 H2O → 2 H2 + O2

Pure water conducts electricity poorly, so a small amount of an electrolyte (something that dissolves into ions, like salt) is usually added to help the current flow.

2. What happens if you electrolyze salty water (brine)?

Salt in water means lots of chloride ions (Cl‑). At an anode these chloride ions can be oxidized to chlorine (Cl2 gas):

2 Cl‑ → Cl2 + 2 e‑

Chlorine gas dissolves/reacts in water to form species such as hypochlorous acid (HOCl) and chloride (Cl‑). Under the right conditions (pH and presence of a base such as NaOH) this can lead to formation of sodium hypochlorite (NaOCl), which is the main ingredient in household bleach:

Cl2 + 2 NaOH → NaCl + NaOCl + H2O

So electrolysis of brine can produce disinfecting chemicals. That is how some commercial hypochlorite or hypochlorous acid generators work in controlled systems.

3. Difference between hypochlorous acid (HOCl) and sodium hypochlorite (NaOCl)

• HOCl is hypochlorous acid, a weak acid and a very effective disinfectant at low concentrations. Its disinfecting power depends on the pH. HOCl is stronger (more effective) than its deprotonated form.
• NaOCl is the sodium salt (hypochlorite ion OCl‑ paired with Na+). In water, NaOCl produces OCl‑ and some HOCl depending on pH.
• At pH below about 7.5 more HOCl exists; at higher pH more OCl‑ exists. HOCl is the species that penetrates microorganisms and inactivates them most effectively.

4. Why you must be careful — safety and hazards

• Chlorine gas is toxic and can be produced if electrolysis of brine is done incorrectly. Even small amounts of chlorine gas are dangerous to breathe.
• Bleach and hypochlorite solutions are corrosive and can damage skin, eyes, metals, and clothing. They can react dangerously with acids or ammonia to form toxic gases (for example, mixing bleach with acid can release chlorine gas).
• Hydrogen gas (produced in electrolysis) is highly flammable. If it builds up in an enclosed area it can ignite or explode given an ignition source.
• Distilled water is not a ready-to-drink upgrade over regular water for everyday use. It lacks minerals; drinking small amounts is safe, but it tastes flat and in extreme cases drinking only distilled water for a long time can change mineral balance.
• Many consumer “generators” are not safe to operate without correct design, materials, and ventilation. Never attempt to build or run a chemical/electrolysis setup at home without adult supervision and proper training.

5. What a countertop water distiller does

A water distiller boils water to make steam, then cools the steam so it condenses back into a separate container. Minerals, salts, and many contaminants that don’t vaporize stay behind in the boiling chamber. The condensed water is called distilled water. Distilled water is useful for laboratory work, some appliances (like irons), or medical uses; it’s not a magic health drink.

6. Hydrogen water and hydrogen water generators

"Hydrogen water" is ordinary water with extra dissolved molecular hydrogen (H2). Some consumer devices claim health benefits of drinking hydrogen-rich water. Scientific evidence for clear health benefits in healthy people is limited and mixed. Key points:

• Electrolysis can generate small amounts of H2 that dissolve in water, but H2 quickly escapes to the air unless it’s stored under pressure.
• Hydrogen gas is flammable, so generating it requires careful equipment to avoid ignition or leaks.
• If you’re curious about claims for hydrogen water, look for peer-reviewed studies and be skeptical of big health claims from vendors.

7. Swimming pools and chlorine chemistry — short version

Pools are commonly disinfected with chlorine-based chemicals (chlorine gas, sodium hypochlorite/bleach, or stabilized chlorine such as trichloroisocyanuric acid). The active disinfecting agents are HOCl and OCl‑; their effectiveness depends on free chlorine concentration and pH. Pool chemistry is a balance of sanitizer, pH, alkalinity, and stabilizer. This is why pool maintenance is usually done with tested dosing instructions rather than guessing.

8. Mel Science kits and safe learning

• Mel Science chemistry kits and similar educational kits are designed for safe, supervised experiments. They include instructions and safety guidance. Always follow the manual and an adult supervisor.
• These kits are a great way to see electrolysis demonstrations, color changes, and basic chemical reactions without dangerous byproducts—because the experiments are chosen to be safe for beginners.

9. What you can do safely (recommended)

1. Do the electrolysis or electricity experiments that come with your Mel Chemistry & Electricity kit, with an adult. Those experiments are designed to teach the basic ideas without producing toxic gases.
2. Observe a distillation demonstration at school or from a teacher—watch steam condense into a clean beaker.
3. Read about pH and acid/base behavior, and do safe pH indicator experiments (red cabbage indicator, litmus) under supervision.
4. If you are interested in pool chemistry, learn how pH and chlorine levels are measured and why testing and controlled dosing is important. Don’t try to make your own pool sanitizer at home.

10. Short summary

Electrolysis uses electricity to split molecules and can produce hydrogen, oxygen, and—when salt is present—chlorine-containing disinfectants. Hypochlorous acid (HOCl) is the most effective chlorine-based disinfectant at certain pH values; sodium hypochlorite (NaOCl) is the main ingredient in bleach. Distillation removes minerals and many contaminants by boiling and re-condensing water. Hydrogen water is water with dissolved H2; claims about health benefits are not well established. All of these processes involve real hazards (toxic gases, flammability, corrosivity), so you should only explore them using supervised educational kits, teacher-led lab time, or commercially certified devices.

If you want, tell me which specific kit or experiment you have (exact Mel Science kit name or the model of a generator), and I will explain what happens in that kit step by step and what safety gear and supervision you should use.