Water Pressure Problems In Apartments

A tenant says the shower has gone weak. That is the whole brief, and it can mean six different things.

First question: is it one tap or everything

This single check does most of the diagnosis.

One outlet only. The fault is at that fixture. A blocked aerator, a partly closed isolation valve, a failed mixer cartridge, or a kinked flexible hose. Cheap, quick, and entirely inside the apartment.

Hot water only. The problem is on the hot side. A tempering valve, a failing hot water unit, or sediment in the outlet. If the building has central hot water it may not be the apartment's fault at all.

Everything in the apartment. Something upstream of the apartment is restricting flow. Usually the apartment's own [isolation valve](/blog/isolation-valves-and-why-a-building-needs-them) partly closed after earlier work, or a failed pressure limiting valve.

Every apartment in the building or a whole stack. Common property. A pump fault, a failed pressure reducing valve on the main, a partly closed main valve, or corrosion narrowing the pipes.

Pressure and flow are not the same thing

Worth separating, because the fix differs.

Pressure is the force in the pipe. Flow is how much water actually arrives per minute.

You can have good pressure and poor flow, and that is almost always a restriction: a narrowed pipe, a part-closed valve, a blocked filter. A pressure gauge on a hose tap tells you one half of the story, and a bucket and a stopwatch tell you the other.

Where the pressure reads fine and the flow is poor, the problem is nearly always something choking the line rather than the supply itself.

The usual causes in older buildings

Galvanised steel pipe. In buildings from the middle of last century, the original pipework corrodes from the inside. The bore narrows over decades until flow drops noticeably. Nothing fixes it except replacement, which is a [stack replacement](/blog/plumbing-stack-replacement-in-older-buildings) conversation.

Pressure limiting valves past their life. They are a wearing part with a service life, and they fail closed as often as open. Frequently missed because nobody thinks to check one.

Pump faults in taller buildings. Buildings above a certain height boost the supply. A failed pump, a waterlogged pressure vessel or a faulty controller shows up as weak pressure on the upper floors first.

Scale and sediment, particularly on the hot side and particularly in mixers and aerators.

Work done recently. A valve left part closed after a repair is one of the most common causes of a sudden change, and it is the first thing to rule out when pressure dropped the same week something else was fixed.

Sudden versus gradual

A gradual decline over years points at corrosion or scale.

A sudden change points at a valve, a failed component, or work done somewhere in the building. Ask when it changed, and ask what happened that week.

Who pays

The pipework inside the apartment from the isolation valve onward is generally the lot owner. The common supply, pumps and mains are generally the strata.

Which is why establishing where the restriction sits comes before the quote, not after. It is the same boundary question as [common property or lot owner](/blog/common-property-or-lot-owner-who-pays).

What we do on a call like this

Test pressure and flow at multiple points, check the apartment's isolation valve, strip and check the fixture, then work back toward the main until the restriction shows itself.

Reporting back with where the fault sits, not just that there is one, is what lets an agent or a building manager decide what happens next.