Onion Hydrosol: What It Is, Why It's Trending, and How to Make It at Home

Onion hydrosol is the water that comes off a still when you distill onion. It is clear, it smells strongly of onion when fresh, and it has become a search term in 2026 because a shampoo brand put it in the product name. If you have wondered what it actually is, and whether you can make it at home, this is the plain version.

The short answer: yes, any copper alembic still makes it in an afternoon, it is one of the least pleasant-smelling things you will ever distill, and there is very little research behind the hair claims. We make stills, so we will tell you how it is done and leave the promises to other people.

TL;DR

• What it is: steam-distilled onion water. Water-soluble sulfur compounds from the onion, carried over with the steam, no oil layer worth collecting.
• Why it is trending: a hair-care brand launched an onion hydrosol shampoo and the searches followed. Most people asking about it have never seen the liquid itself.
• Can you make it: yes, in a 5 litre copper still on a kitchen stove. Expect the kitchen to smell of onion for the afternoon.
• What we can honestly say: it is a rinse ingredient with a long folk history and thin evidence. Patch test, dilute, and do not expect miracles.

What is onion hydrosol?

A hydrosol is the condensed steam from distilling plant material. With lavender or rose you get a fragrant water and a film of essential oil on top. With onion you get the water alone: onions carry almost no essential oil, but they are rich in volatile sulfur compounds, and those come over with the steam. That is why onion hydrosol smells exactly like a cut onion when fresh and why the shampoo makers pair it with rosemary and mint to cover it. Left open in a jar for a day, the sharpest notes fade.

It is not onion juice. Juice is pressed, cloudy, full of sugars and enzymes, and spoils in days. A hydrosol is distilled, clear, and keeps for months in a clean sealed bottle in the fridge, like any other hydrosol.

Why is everyone searching for it?

Onion juice rinses for hair have been a folk remedy in South Asia for generations. In 2026 a hair-care brand released an onion hydrosol shampoo, reviews spread, and the term jumped from nowhere into the same search lists as rose water and rosemary water. Search interest for a product name does not tell you much about the ingredient, so treat the trend as a reason to try a small batch, not as a verdict.

How to make onion hydrosol in a copper still

This is a normal hydro-distillation run. The only special step is the cleaning afterwards.

1. Quarter three or four medium onions, skins on or off, and put them in the pot of a 5 litre copper alembic with about two litres of water. Do not pack it; onion needs room.
2. Seal the head with flour paste, start the cooling water through the condenser, and bring the pot up gently. Onion foams if you rush the heat.
3. Collect the first 300 to 500 ml. That first portion carries most of the aromatics; the rest is increasingly plain water.
4. Bottle in clean glass, label it, and keep it in the fridge. Give it a day open before you judge the smell.
5. Clean the still straight away: a warm water flush, then a citric acid wash, or the next run will taste of onion. Our cleaning guide covers the citric wash.

The same run works for garlic, leek and chive, and everything above about the smell applies twice over.

How people use it

As a diluted rinse after shampoo, a few tablespoons in a cup of water, or mixed into a rosemary hydrosol mist to soften the smell. We are not going to tell you it grows hair. The published research on onion juice and hair is small and old, and there is none on the hydrosol specifically. If you have sensitive skin, patch test on the inner arm first, as with any sulfur-rich botanical.

What we see most often at CopperHolic

Nobody buys a still for onion water, and nobody should. What we do see is owners who bought the still for lavender or rose water using it to test every kitchen trend that comes along, onion included, because a run costs them an afternoon and a citric wash. That is the real case for owning one: the trend changes every season, the still does not.

A still is a tool for curiosity. Onion hydrosol is what curiosity looks like on a Tuesday.

What we recommend

If you want to try it, use the smallest still you own; the 5 Litre is plenty and cleans fastest. If you are choosing your first still and onion water is on the list, buy for the things you will make every month, rosemary, lavender, rose, and treat onion as an experiment. The size guide compares the three sizes, and rosemary water vs hydrosol vs oil explains the rosemary side of the same shampoo label.

FAQ

Does onion hydrosol smell like onion?

Yes, strongly when fresh. The sharpest notes fade after a day with the lid off, and a rosemary or mint hydrosol mixed in covers the rest. Onion hydrosol shampoos are scented for the same reason.

How long does onion hydrosol keep?

Months in a clean, sealed bottle in the fridge, like other hydrosols. Discard it if it turns cloudy or the smell changes. Our hydrosol shelf life guide covers storage.

Will it make my still smell of onion?

For one run, yes. A warm flush and a citric acid wash straight after the run clears it. Do not leave onion water sitting in copper overnight.