The Science Behind Splash

Water utilities add a disinfectant — usually chlorine or chloramine — to kill germs and to keep water protected as it travels through miles of pipe. Disinfection is a large part of why tap water is safe to drink.

That protection is designed to last. A small residual stays in the water all the way to your tap, so it is still present when you turn on the shower. In the United States, chlorine is regulated at a maximum residual disinfectant level of 4 mg/L, and water within those regulated limits is not considered dangerous.

Free chlorine is, by design, a reactive oxidant. It reacts with the materials it meets: organic matter in the water, pipe surfaces, and whatever it touches downstream. Some people find chlorinated water drying or irritating on skin and hair. That experience is not the same thing as a health hazard at regulated levels, and sensitivity varies from person to person.

A shower filter is not a medical device and does not make water safer to drink. What it can do is reduce free chlorine in the water that reaches your showerhead — a narrow, specific job.

Your skin’s outermost layer, the stratum corneum, is a barrier. Lipids between the skin cells hold water in and help keep irritants out. When that barrier is intact, skin tends to feel comfortable. When lipids are depleted, it can feel tight and reactive.

Everyday washing works against that barrier a little. Hot water lifts lipids, and surfactants from soap and body wash can leave residue behind after rinsing — a mechanism that has been studied independently of what else is in the water.

Water chemistry adds another variable. In a controlled study of 80 participants, washing with harder water left significantly more surfactant on the skin, which increased water loss and caused irritation — particularly in people with atopic dermatitis who carry filaggrin mutations. The same study did not observe a clear effect from chlorine, and its authors said so plainly.

So the mechanism is published, but the product evidence does not exist yet. Splash does not claim that our filter treats eczema, prevents irritation, or restores the skin barrier.

Hair is a protein fibre wrapped in overlapping cuticle scales. How it feels and behaves depends on water chemistry, how often you wash it, the temperature of the water, and the products you use.

Hardness minerals behave quite differently from disinfectants. Hair takes up calcium and magnesium from water: one study found samples became notably loaded with hardness metals even at moderate levels, accumulating mainly at the cuticle. Another found a measurable decrease in tensile strength after hard-water treatment in the laboratory.

Both findings describe fibre behaviour under controlled conditions. Neither measured shine, softness or how hair looks in daylight, and neither tested a shower filter.

We are not going to promise stronger, shinier or healthier hair. What we can say is that what touches your hair is worth understanding, and that hardness is part of that picture even when chlorine is reduced.

Hard water is water that has picked up dissolved calcium and magnesium as it moved through soil and rock. The USGS describes hardness in milligrams per litre as calcium carbonate: 0–60 is soft, 61–120 moderately hard, 121–180 hard, and above 180 very hard.

Those dissolved minerals are what leave scale on glass, tiles and fixtures, and what react with soap to form scum. That is why hard water needs more soap to lather and can leave a film behind on skin and hair after rinsing.

Softening takes ion exchange or a comparable process, and most standard shower filters do not do it. Our cartridge is not a softener. If that ever changes and softening is verified for the finished product, we will publish the test result alongside the claim.

Filtration media can reduce free chlorine by adsorbing it as water passes through. Carbon fibre, activated carbon and similar media are used for this, and how much they remove depends on how much media there is, how it is packed, and how long the water stays in contact with it.

Our proposed cartridge pairs a carbon-fibre layer with other media. The composition is not final, so we describe it as proposed rather than as a specification.

Performance then depends on your water and your shower: cartridge composition, the chemistry of your water, flow rate, temperature, and cartridge age. Change one of those and the result changes, which is why blanket claims about shower filters are unreliable.

NSF/ANSI 177 is the standard that verifies free available chlorine reduction in shower filtration systems, tested for one finished product at a stated capacity and flow rate. It covers chlorine only — not hardness, skin or hair — and the Splash cartridge has not been certified to it yet.