Designing cold water systems to avoid leaks

Water leakage is one of the major problems in buildings in Hong Kong. It poses a health problem for occupants – both physical and in terms of mental stress – and causes structural deterioration to the building as well as damage to the building’s internal finish. According to a study from Hong Kong Special Administrative Region (HKSAR) Government Legislative Council Secretariat in 2019, there were 36,684 complaints about water damage the previous year, up by 43% from 2010.

Common causes of water leaks in buildings are:

• bad design

• poor workmanship

• inappropriate usage of construction materials

• deterioration of materials

• inadequate maintenance

• improper usage/ decoration progress

• deteriorated waterproofing around baths, showers and bathroom walls

• leakage from water supply pipes of the flat or surrounding flats

• leakage from the drainage pipes of the flat or surrounding flats

• leakage of waste water or rain water through the building envelope such as the roof/external wall

In this article we discuss some essential design and operation measures to prevent water leaks.

1. Positioning and fixing requirements for pipework

In accordance with Water Supplies Department’s (WSD) regulation, no water pipe shall be embedded within load-bearing structural elements (such as columns, beams and slabs) in a longitudinal direction. However, for aesthetic reasons, plumbing pipework is often concealed – for example, in screed (see figure 1, above), under tiles, in internal (non-load bearing) walls, in recessed openings or under a suspended floor, where it is easy to access.

2. Provision of drip trays with leak detection for water-sensitive areas

Normally, engineers should avoid locating water pipes in water-sensitive-areas – for example, rooms full of computers. However, sometimes this is unavoidable. Drip trays are a cost effective and simple solution that helps reduce the risk of water ingress. In addition, drip trays can be installed with a water leak detection and locating system (see figure 2, above) to give an early warning and help the tradesperson to locate leaks quickly and accurately. These systems raise an alarm that gives an accurate location of a leak at a specific zone within the drip trays.

Alternatively, to enhance protection for the room and its contents, the tray can be enclosed or even take the form of a pipe-within-pipe structure (see figure 3, above).

These allow an alert to be sent to the building management team, allowing the pipe to discharge to a more conspicuous position, and can be supplemented with an audio-visual warning device to reduce the searching time and tackle the incident as quickly as possible.

3. Adoption of innovative automatic meter reading (AMR) system

With the adoption of an AMR System, we can record and monitor historical metering data, status outputs and alert signals for water meters. The infrastructure of the system consists of AMR outstations and the AMR primary station (see figure 4, above). The AMR primary station and the smart water meters, including primary meters and check meters (if any) will be provided by the WA. The purchaser/grantee will need to supply (except for smart water meters), install and commission the AMR outstation according to the requirements specified by the WA.

The data is automatically sent to WSD through the local Global System for Mobile Communications (GSM) network for analysis to help identify early signs of leaks in the mains. Remedial works are arranged according to the analysis results so that potential leaks can be promptly located for repair.

In utilising similar technology, the meter reading can include further analysis and interface with other systems to enhance leak protection features, such as alerts for:

• in commercial buildings, abnormal water flow and /or demand after operating hours, during long holidays or in areas without occupancy through the security/ access control system

• unusually large and continuous duration of high demand.

These could be signs of a water leak and the building management team should act on the information straight away, or shut off the water supply when abnormal readings are found, to minimise the risk of water damage. This is especially important in commercial premises with computer rooms and/or a raised floor system.

4. Precise design to control supply pressure

Most buildings in Hong Kong are high rise and indirect water supply is normally designed with gravity by dividing the building into several water supply zones (see figure 5, above). Water pressure varies in the supply zones depending how far a consumer’s end point is from the roof tank. Consumers in lower accommodation receive water at higher pressure which means that pipes and fittings are prone to leaks, especially if there are system design faults.

Supply pressure design is highly effective in reducing leaks. In implementing pressure control, it is essential to properly install the interim break tank and pressure reducing valves to limit the pressure and maintain a zone with supply pressure between 2.0 and 4.5 bar or 5.5 bar preferably. The key challenges are finding adequate spaces for installing the water tanks and selecting the appropriate equipment, pipework and valve pressure rating.

The narrower the water supply pressure range the easier it will be to control the system pressure and lower the risk of leaks. At the same time, less water flow demand through the sanitary fittings helps to save water. Therefore, it is recommended to fit secondary pressure-reducing valves to control the water supply pressure, serving both purposes.

5. Visual inspection of pipework for leaks and adequate support

Visual inspection of pipework should be conducted during regular maintenance to check if there are:

• any physical signs of leaks, such as water around joints, water on floors or discolouration of fittings;

• adequate fixing supports, or whether there are missing or broken pipe supports and brackets;

• damaged or vandalised pipework.

Where pipes are concealed, checking for damp patches on walls and ceilings can help to detect any leaking pipes.

6. Proactive leak control by inspection

The investigation process should include an investigation request, desktop study, initial basic inspection of affected areas, detailed site investigation and survey, analysis and compilation of findings to establish sources and causes, and preparation of the investigation report.

Existing methods adopted by various government departments include:

Visual inspection, moisture meter test, water ponding/ colour water test with or without chemical tracer to roof slab, internal floor slabs or in-situ made shower trays, colour water test (CWT) on drainage outlets/sanitary fittings and colour water spraying test on peripheral walls of bath tubs/shower trays, salinity test, reversible pressure test (RPT) and water meter flow test.

Some other testing methods are also recommended:

(i) Static pressure test

Measures hydraulic water pressure to a section of pipeline to test any drop of static water supply pressure over a period of time. (Pressure drop = leakage in the test system)

Suitable if the section of pipeline can be isolated.

(ii) Acoustic leak detection method

A leak will cause vibrations to the pipes and an emission of high frequency sound due to rapid release of energy from localised source (see figure 6). Thus, it can verify the location of leaks in long pipes. Suitable if there is a long section of concealed pipeline.

(iii) Infra-red thermographic test

Evaluate presence of water leaks or moisture penetration by electromagnetic wave. Water has a higher specific heat capacity.

• Wet areas: relatively colder areas in the infrared images

• Examine the difference in temperature relative to the rest of the finishing surfaces.

Suitable for all general cases where the pipeline is near the surface.

(iv) Microwave concrete sub-layer moisture content test

Measures the relative moisture content and distribution in certain levels of depths on pre-designed gridlines of the seepage areas by Moist R1: 0-30mm, R2: 0-70mm, D: 0-110mm, P: 0-300mm & S: 0-800mm.

Suitable in cases where it is difficult to reach a concealed section of pipe.

(v) Radar scanning

Send short pulse of electromagnetic energy into the material. Radar measures the time taken for a pulse to travel back and forth from the target.

Suitable in the case of long concealed pipelines and where you can access the whole section, by maintenance hole/inspection chamber only.

(vi) Fourier Transform Infrared (FTIR) Micro-spectroscopy Inspection

FTIR is a material identification technique which works by analysing the infrared absorption spectrum of the materials to identify the presence of colour dye particles used in CWT, spray test or PT.

Suitable in cases where there is a reachable section of pipeline.

(vii) Electrical capacitance and resistance tests

Electrical capacitance test

• Electrical capacitance is the ability of a body to store charge.

• The test works by measuring the changes in this ability in the object. The wetter the material, the greater the response.

Electrical resistance test

• Apply a voltage across two points and measure the current/ electrical resistance. The wetter the material, the smaller the resistance

Suitable in cases where it is hard to identify where the leak has occurred. Remedial works can be arranged according to the analysis results so that potential leaks can be promptly located for urgent repair.