Water Pressure in Auckland Homes, and Why It Is Highest at Night

Water pressure is the one plumbing variable that touches everything else in your house. It decides how your shower feels, how long your tapware lasts, and whether the fitting behind your vanity gives up at three in the morning.

Most people only think about it when it is too low. The more expensive problem is when it is too high, and the reason so many failures happen overnight is not a coincidence.

Why is my water pressure stronger at night?

Because everybody else has stopped using water.

Pressure at your house is what is left after the network has pushed water through kilometres of pipe to get there. During the day, thousands of homes, plus every commercial and industrial user in the area, are drawing at the same time. All that flow creates friction in the mains, and friction eats pressure. What arrives at your boundary is the network pressure minus everything lost getting it to you.

At night the demand disappears. Houses are asleep, and the factories and businesses that draw large volumes during working hours are shut. Flow in the mains drops to a trickle, so almost nothing is lost to friction, and the reservoirs feeding the area are at their fullest after refilling overnight. The pressure standing at your meter in the small hours is the highest it gets all day.

Nobody is running a tap to feel it. But every pipe, fitting, hose and washer in your house is holding it back.

Does that actually break things?

It is why so many burst pipe calls come first thing in the morning.

A fitting that is corroded, a flexi hose with a failing braid or a washer that has gone hard will usually cope with daytime pressure. Sitting against peak overnight pressure for six or seven hours is a different test, and that is when marginal ones let go. The homeowner is asleep, so nothing gets shut off, and the water runs until somebody comes downstairs.

The same effect explains the more harmless version people ask us about: a hot water cylinder that only discharges from its relief line overnight, or a tap that drips at night and not during the day.

What is normal, and how do I find out what mine is?

Pressure is measured in kilopascals. As a rule of thumb, tapware, mixers and appliances are generally designed around a maximum of about 500 kPa at the fixture, and that is the figure limiting valves are typically set to.

Network pressure at the boundary is often well above that, and it varies enormously across Auckland. Where you sit relative to the local reservoir is the main factor, so a house low in a valley can see far more pressure than one on a ridge a kilometre away. Your neighbour’s experience is not a reliable guide, and neither is the pressure at your old house.

The only way to know is to measure it, with a gauge on an outside tap. It takes a couple of minutes. If you want the number that actually matters, it needs measuring at night or with a gauge that records the maximum, because a daytime reading understates the peak.

What is a pressure limiting valve, and do I need one?

It is a brass valve fitted on the incoming line, ideally right after the meter, that caps the pressure entering the house regardless of what the street is doing. Everything downstream then lives within what it was designed for.

Older Auckland houses very often do not have one. If your house was plumbed before limiting valves became standard practice, and nobody has renovated since, assume you do not have one until you have looked. On a job in Glenfield where we installed a new water main, we fitted a limiting valve at the start of the new line while the trench was open, which is the cheapest time it will ever happen.

It is not just about preventing bursts. Constant high pressure shortens the life of tap washers and cartridges, stresses every flexi hose in the house, makes mixers noisy, and wastes water at every fixture.

Do these valves fail?

They do, and they are not a fit and forget item.

We took a Saturday after hours call in Panmure where the pressure limiting valve at the property’s water entry point, mounted in the garage wall, was leaking continuously. The valve was faulty and could not be left, so we isolated the supply and replaced it. That is a fairly typical way for them to end: not by quietly ceasing to limit, but by weeping.

The quieter failure is worth knowing too. At a property in Mount Wellington the call was about a hot water cylinder discharging out to the roof outlet. The cause was on the valve side rather than the cylinder, so we replaced the pressure reducing valve and the relief valve as a matched pair and adjusted the aerators on the mains pressure fixtures to suit. Water running out of the pipe on your roof is very often a pressure story rather than a cylinder story.

If your valve is more than about ten years old, or you have never seen it, it is worth having someone look at it.

My pressure is too low, not too high

That is a different problem with a different set of causes: a partly closed valve, corroded galvanised pipe narrowed by rust, an undersized supply line, a blocked aerator, or a low pressure cylinder feeding fixtures that expect mains pressure. We have written about the common causes of low water pressure separately.

One thing worth flagging: if your pressure has dropped suddenly rather than always been poor, that can point at a leak somewhere between the meter and the house. Check the meter with everything off before assuming it is a fixture problem.

Not sure what your pressure is doing? Give us a call. Measuring it is quick, and it tells you whether you are protecting the plumbing you already have or paying to replace it a fitting at a time.

Common questions

Can I test my own water pressure?

Yes. A pressure gauge that screws onto a garden tap is inexpensive and available at any plumbing supplier. Screw it on, open the tap fully with nothing else running, and read it. Bear in mind that a reading taken in the middle of the day is the low point of the cycle, so if the daytime number is already high, the overnight peak will be considerably higher.

Will a limiting valve make my shower worse?

Generally no, because flow and pressure are not the same thing. A limiting valve caps the pressure to what your tapware was designed for, and modern mixers deliver a good shower at that pressure. If a shower genuinely feels weak afterwards, the usual culprits are a blocked shower rose, a restrictor in the fitting, or a valve set lower than it needs to be, all of which are easy to adjust.

Why does my cylinder discharge water only at night?

Because that is when the incoming pressure peaks. A relief valve opens when pressure exceeds its rating, so a system sitting close to the limit all day will tip over it in the small hours. A little discharge as water heats and expands is normal; a steady overnight discharge usually means either the valve is failing or the incoming pressure is too high, and both are worth sorting rather than ignoring.

Is high pressure covered by insurance if it causes a burst?

The burst itself is normally treated as sudden accidental damage, so the resulting damage is usually claimable. Where it gets awkward is if the same fitting has failed repeatedly, because that starts to look like a known condition rather than an accident. Fixing the underlying pressure is the way to keep the situation firmly in the accident category.

Where should the valve be fitted?

As close to the point where water enters the property as practical, so everything downstream is protected. Right after the meter is the standard position, and on a new main that is straightforward. In an existing house it often ends up at the entry point into the building instead, which is why you will sometimes find one in an access hatch in a garage wall. Wherever it is, it needs to be reachable, because it will eventually need replacing.