Aerator and jet regulator: the difference and which size fits

A jet regulator is the component that sits at the outlet of the tap and mixes air into the water. The same component is called a Perlator when it comes from Neoperl: the name is a registered trademark, not a technical term. The manufacturer lists M22 and M24 as standard threads, each as a female and as a male thread.

That answers the most common question. The second most common concerns the size on your own tap. The diameter is measured with a calliper or a ruler and checked against the table further down. It takes longer to read than to do.

Two values are decisive: the type of thread and the diameter in millimetres. On a male thread, the teeth point outwards; on a female thread, they point inwards. On a male thread, the diameter is measured across the outer edge of the teeth; on a female thread, across the inner edge. A calliper is more accurate than a ruler, but a ruler is usually sufficient for matching the size.

The following table comes from the measurements in the Alb Filter thread guide. It matches the measured value to the trade designation. The measured value is always below the number in the name, more clearly so for female threads than for male threads. So look up the measured value in the table instead of rounding it yourself.

The number after the M stands for the nominal diameter. In its manufacturer overview, Neoperl lists M16, M16.5, M18, M18.5, M20, M21.5 and M24 with a pitch of 1 millimetre. In addition, there is M24 with 1.5 millimetres, as well as inch threads and special North American threads. Special sizes are usually only available to order.

Different connections apply to bath spouts and to kitchen taps with a pull-out spray. If you need an adapter, you will find the right match in the thread guide.

Jet regulators are standardised. DIN EN 246 bears the title “Sanitärarmaturen, Allgemeine Anforderungen an Strahlregler” (sanitary tapware, general requirements for jet regulators) and is available in the October 2022 edition. Before that, the November 2003 edition applied. The standard covers dimensions, hydraulics and mechanics, as well as noise behaviour and the associated test methods.

The flow rate is set out in a separate table in the standard, which divides jet regulators into flow classes. We do not give the figures for these flow classes here, because the text of the standard is only available for a fee. We do not have a freely accessible primary source with the complete class limits. Anyone who needs the values will find them in the manufacturer's data sheet.

Another specification matters when buying: flow rates refer to a flow pressure of 3 bar. A jet regulator with 6 litres per minute delivers less at lower pressure. Models with a constant flow regulator compensate for this and keep the volume almost constant over a wide pressure range.

Neoperl gives 4 litres per minute at the washbasin, 6 in the kitchen and 8 in the shower as a guide for water-saving taps. All three values apply at a flow pressure of 3 bar. You can measure for yourself whether your own tap is above this: hold a measuring jug under the fully opened tap and time how long it takes to fill 1 litre.

There is no reliable percentage figure for the savings, and there is a reason for this. The savings depend on what flowed before, and this starting value varies from tap to tap. Figures such as “up to two thirds” are circulating, but they cannot be verified against any independent primary source. Your own measuring jug is more meaningful here than any rule of thumb.

The lever behind it is real nonetheless. The Umweltbundesamt (German Environment Agency) puts drinking water consumption for 2022 at 126 litres per person per day. According to the Verbraucherzentrale (German consumer advice centre), 4% of this is used for cooking and drinking, while the large remainder flows through taps, the washing machine and the toilet. It considers 70 to 100 litres per person per day to be economical.

The energy advice service of the Verbraucherzentrale gives a documented comparison figure for the shower. According to it, around 20 litres per minute flow through a shower head. With a flow restrictor or an aerator, the value drops to 8 to 10 litres. The same source names precisely this as the limit of the measure: water-saving shower heads are unsuitable for non-pressurised storage water heaters and instantaneous water heaters, because the normal flow pressure must be maintained.

With hot water, the smaller volume also saves the energy needed to heat it. However, these 20 litres per minute apply to the shower head. At the washbasin and in the kitchen, the values are significantly lower, which is why the savings there cannot be quantified without measuring them yourself.

Limescale build-up is a deposit on the screen that forms when hard water evaporates at the outlet. The stream then becomes uneven, sprays to the side or noticeably weakens. How quickly this happens depends on the hardness of the local water. The water supplier publishes this value. You can find out more in the guide to limescale in water.

To descale, unscrew the component and place the individual parts in a solution of household vinegar and water in equal parts, or in citric acid. A common recommendation is to leave them to soak overnight. The rubber seal suffers from prolonged contact with acid; a replacement costs a few cents and should be part of every cleaning.

One variant works without unscrewing. A bag of descaling solution is attached to the tap with adhesive tape so that the liquid surrounds the component. This helps with light limescale build-up. If the jet regulator is stuck or the screen is clogged, there is no way around removing it.

The jet regulator sits in a legally remarkable position. In § 10, the Trinkwasserverordnung (German Drinking Water Ordinance) stipulates that the requirements for drinking water must be met “at the outlet of the tapping points for drinking water”. That is the spout of the tap, i.e. precisely the point where this component sits. The ordinance does not mention the jet regulator itself anywhere.

It is revealing how experts handle this. For systemic testing for legionella, the Umweltbundesamt's recommendation of 13 October 2025 prescribes the following as the first step of sampling: “removal of jet regulators and other devices”, followed by disinfection of the outlet, preferably by flaming. Only then does the approved testing laboratory take the sample. The recommendation was issued following consultation of the Drinking Water Commission; the procedure itself follows DIN EN ISO 19458.

The reason for this is obvious. The systemic testing is intended to assess the drinking water installation in the building, not the component at its end. Anything fitted to the outlet itself would distort the result. Conversely, anyone who wants to know what is clinging to the tap needs a different procedure. For this purpose, the same recommendation provides for sampling at tapping points “as the water is used”. This makes it possible to detect local contamination at the tap fitting.

For households, this is no cause for alarm, but it has a simple consequence: the component should be cleaned regularly, and the seal should be replaced at the same time. This applies in particular after prolonged stagnation, for example if a flat has stood empty for weeks. How water samples work at home is explained in the guide to water quality.

A jet regulator is a component for shaping the stream, not a filter. The screen holds back coarse particles, but has no effect on limescale, dissolved metals and organic trace substances. If you want to filter at the tap, you replace the component with a filter that fits the same thread.

This is exactly where the size question becomes practical. A tap filter is fitted at the same point where the jet regulator was, and therefore needs the same thread specification. If you know the measured value from the table above, you will find the right adapter in the thread guide – and often find that you don't need one at all.

What a filter at the tap can and cannot do depends on the cartridge. You will find an overview under water filters for the tap, and installation instructions in the guide to installation.