Flushing water pipes after a shutdown: what reopening day takes

In a closed wing every outlet counts on its own

For your own flat, that advice is right. The Umweltbundesamt (German Environment Agency) recommends a short run-off for water that has stood in the pipe for four hours or more, until you can feel it turn cooler.

After three weeks away you simply let it run longer, once at every tap. Three taps, ten minutes, done.

Now try the same thing in a hotel: a wing of 60 rooms that stayed shut over the holidays. That is not three taps; it is 60 showers and 60 basins, plus the hand shower over the bath, the staff shower in the basement and the cleaner’s sink in the store cupboard.

There is no central purge that clears the whole wing in one go. Every outlet gets its own turn, fully open and running long enough to replace what is sitting in the pipe. Within that round you do open several outlets together, because the distribution pipes only see enough flow that way. It still leaves 60 showers to work through; one person covers a corridor in a morning.

On top of that, you are operating an installation that has to run in line with the generally recognised technical rules, as the Trinkwasserverordnung (Germany’s drinking water ordinance) requires. So reopening day needs a plan, not good intentions. We have explained which showers in a building are actually affected elsewhere.

Flushing water pipes after a shutdown: it comes down to how long

The 72 hours are in the standard. The number you are missing on reopening day is in your occupancy plan: how long has nothing flowed at this outlet? Water has to be exchanged at every point of the installation at least every 72 hours, through use or through deliberate flushing, as VDI 6023 Part 1 (the German hygiene standard for water installations) requires.

The clock runs at each outlet separately. That is why a well-occupied building can still have thirty showers that have been dry for months, and why the question of when the 72 hours actually start is anything but academic.

Classification based on VDI 3810 Part 2 / VDI 6023 Part 3 (Table 2), DIN EN 806-5 and DVGW worksheet W 551-3 (A). Own illustration.

If an area has stood still for a long time, you will usually need a water sample as well, taken and analysed by an approved testing body. Where that line sits depends on the building, so settle it with the Gesundheitsamt (local public health authority) while the area is still running.

Before a reopening, then, the first thing that counts is how long the water in each area has stood. How long you flush follows from that.

When does your own flushing round stop being enough?

Beyond seven days it is not the same work any more. Now the pipework gets a cleaning flush: aerators and shower heads come off, and the water runs at a far higher flow rate than in a routine flush.

That is work for a specialist contractor, not for the maintenance technician with a bucket. Disinfection only comes into it if a microbial contamination is found.

Who takes the first shower after the closure

On reopening day there is a person at the end of every pipe. In a care home, an 85-year-old moves into the room that stood empty. In a hospital, the person stepping into the shower is a patient still under treatment.

None of that is meant to sound dramatic, but it is why the order you work in on reopening day is not arbitrary. Sort the running order by occupancy.

The outlets that will be used on opening day come first. And no room goes back into use before water has run at its shower and basin. Take the floors in order instead of the occupancy list, and by mid-morning you are handing over rooms where no water has run yet.

Then there is the calendar. A specialist contractor needs booking well ahead: reopen in September and start phoning round in September, and you open with standing water in the wing.

In a care home or a hospital, a gap like that usually turns up mid-year, at a single room. It stands empty for six weeks and is then reoccupied at short notice, and if you keep a record of the vacancy you see it coming.

Reopening day, step by step

Flushing runs in the direction of flow, from the incoming main out to the furthest outlet, so that fresh water really does travel through the whole network. Cold and hot are done separately.

“Every” is meant literally, from the hand shower over the bath to the staff shower in the basement. Skip one door and the water behind it never moves. The log still shows it as flushed.

Wherever water sits still, you have exactly the conditions Legionella need to grow. Warmth and stagnation, nothing else.

At home nobody asks you for a piece of paper. In a building, the operator has to be able to show what actually ran, and there is a set of rules of its own for taking an installation out of service and back in, template log sheets included.

A flush nobody wrote down with a date and an outlet is a flush you cannot prove.

How to keep stagnation times short in the first place

Close an area and you have three options.

You can leave everything standing and pay for the cleaning and disinfection at the end. You can keep flushing by hand, which works as long as somebody really does walk the round through the empty wing, every week, in February too. Or you can take the area out of service and back into service as planned, with the section shut off and with the documentation that goes with it.

For the showers there is a fourth: don’t let the rhythm break in the first place. Aqvior is a surface-mounted shower fitting (Aufputz-Duscharmatur) with built-in Legionella flushing. It goes onto the existing connection without a bathroom renovation, in under an hour.

The flush duration is set once at commissioning and runs the same way every time after that, logged with timestamp, duration and water temperature in the web dashboard. That is prevention. Aqvior does not clean up a positive result, and it does not replace the Legionella test. Can a fitting take on the cleaning and disinfection after seven days? No, not even an automatic one. Basins, WCs and kitchen taps keep their own routine. What it does is keep the shower from getting that far.

What changes is where you start on reopening day. A shower that stayed in rhythm through the closure starts the day at 72 hours, not at four months.

Frequently Asked Questions

We are closing a wing over the winter. Is shutting the riser valve enough?

No. Shutting off is only one of the steps, and a closed valve does not remove the water sitting behind it. A planned decommissioning is a procedure in its own right, with fixed steps from the water heater through to the documentation. Turn the valve and do nothing else, and you have moved the work to reopening day.

Do rooms that were occupied during the closure have to be flushed as well?

No, as long as water ran at their outlets at least every 72 hours. What counts is the single outlet: in an occupied room the shower runs daily, while the hand shower in the second bathroom has been dry for weeks. That hand shower belongs on the flushing round.

Does all of this apply to basins, WCs and kitchen taps too?

Yes. The stages by stagnation time apply at every outlet in the building. The shower gets particular attention because drinking water is aerosolised there for minutes at a time, and that is one of the conditions § 31 TrinkwV (Section 31 of Germany’s drinking water ordinance) names for the testing requirement.

Does a long stagnation change anything about the Legionella test?

Not the interval. Where showers and a larger hot-water tank come together, hotels, care homes and hospitals test once a year. A test after a longer interruption belongs to bringing the installation back into service and does not replace the annual one.