Backflow Prevention

Safeguarding Wellington's Water Supply With Backflow Prevention

We provide installation, testing, and repairs, safeguarding water purity. At L B White, our superior backflow prevention maintains clean and safe water, fulfilling our mission to protect this invaluable resource.

What is backflow and do I really need a backflow preventer?

The occurrence of backflow involves the reverse flow of undesirable liquid, gas, or suspended solid into the water supply, leading to water contamination. To mitigate this risk, the use of a backflow prevention device is compulsory in New Zealand. The crucial role of these devices lies in preventing contamination and pollution, prioritising health and safety concerns.

What would happen if I didn't have a backflow Preventer?

In the absence of a backflow preventer, fluctuations in water pressure can result in backflow, allowing the contaminated water used by your system to pose safety risks beyond your family or customers. With sufficient force, this backflow can extend to contaminate the entire town's water supply.

How often must a backflow device be checked?

Following the completion of the initial installation and testing, it is mandatory to undergo a backflow prevention device examination every 12 months conducted by a certified backflow technitian. Sign up for our reminder service and you will be notified by mail when your backflow prevention device is scheduled for its annual test.

What are the two types of backflow problems?

Backflow is an unwanted reversal in the flow of water that can introduce contaminants into your potable water supply. Two primary conditions can lead to backflow: back-siphonage and backpressure.

Back-Siphonage: Back-siphonage occurs when the pressure in the supply system drops below the atmospheric pressure. This can cause the water to flow in the opposite direction and potentially draw contaminants into the potable water supply. Events like a sudden heavy water demand such as firefighting, water main breaks, or system repairs can create conditions for back-siphonage. Back-siphonage can be prevented using devices like an air gap, atmospheric vacuum breaker, or a pressure-type vacuum breaker. Regular maintenance and check-ups from a certified plumber can also ensure that your system is safeguarded against this type of backflow.
Backpressure: Backpressure backflow happens when the pressure downstream is higher than the supply pressure. This pressure differential can force contaminants into the potable water supply. Causes can be attributed to factors like booster pumps, pressure vessels, or elevation changes.To prevent backpressure backflow, one can use a reduced pressure backflow assembly or a double check valve. Regular inspections by certified professionals, like L B White's team of qualified "Plumbers Wellington", can ensure these devices are functioning properly and effectively mitigating backpressure risks.

L B White offers a comprehensive range of backflow services, including:

Backflow Preventer Testing (IQP): Our team performs thorough testing of your backflow preventer to ensure it's functioning as intended and maintaining the integrity of your water supply.

Backflow Preventer Supply and Installation: We provide quality backflow preventers and ensure they're properly installed in your system for optimal performance.

Backflow Preventer Servicing and Repairs: We are committed to maintaining your backflow preventers to ensure they remain in top working condition.

Backflow Preventer Surveying: Our team conducts in-depth surveys to assess the risk of backflow in your system and propose effective preventative measures.

We also cover different types of backflows to ensure that we are addressing your specific needs and circumstances. We deal with a variety of backflow preventers, including reduced pressure zone assemblies, double check valve assemblies, and pressure vacuum breaker assemblies, among others.

DLM Wallace Lead Sheet / Acrylead

Product Description:

DLM Wallace Lead Sheet & Acrylead consist of virgin lead of at least 99.8% purity, machine cast in to sheet form of various dimension and thickness. Acrylead has a factory baked acrylic primer coating which inhibits the contact of water with the lead and its oxides, greatly reducing lead run-off which can cause staining on surrounding roof materials such as tiles. Lead Sheet & Acrylead are soft and malleable, making them a versatile flashing material. They offer strong resistance to corrosion and UV degradation, offering unparalleled longevity of service.

Scope of use:

Lead Sheet & Acrylead are used as a flexible weatherproof flashing to drain or deflect water back outside roof

and wall cladding systems. They are commonly used for flashing concrete, clay and slate tile roofs, for buildings described in Table 1 of NZS 3604:2011, and NASH Standard Part 2: May 2019- 1.3.1.

Relevant building code clauses

· B2 Durability – B2.3.1 (a)

· E2 External Moisture – E2.3.1. E2.3.2

· F2 Hazardous Building Materials – F2.3.1

Contribution to code compliance

B2 Durability – B2.3.1 (a)

When installed in accordance with DLM Wallace literature and NZBC E2/AS1, Lead Sheet & Acrylead will provide durability of no

less than 50 years. DLM Wallace manufactured Lead Sheet has an in-service history in New Zealand of over 100 years.

E2 External Moisture – E2.3.1. E2.3.2

When installed in accordance with DLM Wallace Literature and NZBC E2/AS1, Lead Sheet & Acrylead will contribute to satisfying

the these performance requirements on NZBC E2. DLM Wallace Lead Sheet & Acrylead (17kg/m2 grade and above) meet the requirements of NZBC E2/AS1 4.3.1. DLM Wallace Lead Sheet & Acrylead is manufactured in accordance with AS 1804:1976 (Soft Lead Sheet and Strip).

F2 Hazardous Building Materials – F2.3.1

Prior to working with DLM Wallace Lead Sheet & Acrylead, installers and handlers should familiarise themselves with the health and safety guidelines offered in the DLM Wallace Lead Sheet & Acrylead Material Safety Data Sheet.


DLM Wallace Lead Sheet & Acrylead is manufactured in accordance with AS 1804:1976 (Soft Lead Sheet and Strip).


DLM Wallace Lead Sheet & Acrylead consist of virgin lead of at least 99.8% purity, machine cast in to sheet form of various dimension and thickness. Acrylead has a factory baked acrylic primer applied to both sides of the sheet, which minimises run-off of lead oxides.


· Material compatibility must be considered when specifying and installing DLM Wallace Lead Sheet & Acrylead.

· Lead Sheet & Acrylead must not be used in contact with zinc-aluminium coated long-run steel or zinc- aluminium coated pressed metal tiles.

· Refer to NZBC E2 AS1, Table 21- Compatibility of materials on contact.

· Refer to NZBC E2 AS1, Table 22 – Compatibility of materials subject to run-off.

· Due to thermal expansion and contraction, individual pieces of Lead Sheet & Acrylead must not exceed the dimensions listed in the table below;

Weight (KG/M2)
Maximum Length (MM)
Maximum Girth (MM)

Maximum Size of Individual Pieces of Lead for All Flashing Applications

Installation Requirements:

Nominal Weight (KG/M2)
Nominal Thickness (MM)
Typical Uses
Sound proofing
Apron and cover flashings, hip and ridge
flashings, lead slates, chimney flashings and weatherings to cornices, parapets, full roof cladding, sound proofing, radiation shielding
Sound proofing, radiation shielding
17 (Plain sheet and Acrylead)
Parapet, box a tapered gutters, or situations that
demand extra length

Dlm Wallace Lead Sheet & Acrylead Grades
Flashings Must Be a Minimum of 17KG/M2

· Lap cover between individual sheets/pieces must be a minimum of 100mm

(Refer NZBC E2/AS1- 4.5.2 (f) )

· Parallel flashings must be dressed down in to the tile pan, and have a minimum cover of 150mm, with a minimum upstand of 100mm (75mm minimum upstand behind cladding). Refer NZBC E2/AS1- Figure 26.

· Transverse flashings must have a minimum cover of 150mm over the tile, and have a minimum upstand of 100mm (75mm minimum upstand behind cladding). Refer NZBC E2/AS1- Figure 26.

· Flashings should be designed so that while the lead is in position, free thermal movement is not restricted.

· Nails, screws and fixings should have a similar life expectancy, and thus should be copper, or stainless steel.

· When forming and shaping lead, caution must be taken to not over-stretch the lead, which can create thin areas with reduced integrity.

Maintenance Requirements:

To reduce the risk of run-off staining surrounding materials, a patination oil should be applied to un-painted lead sheet as soon as possible after fixing. Acrylead should be over painted with a quality acrylic external house paint and this coating should be maintained. As with all roofing material, Lead Sheet & Acrylead should be kept clean and free of moss, mould, lichen and


Warning and Bans:

DLM Wallace Lead Sheet & Acrylead is not subject to warning or ban under section 26 of the Building Act 2004.

Types of Products

There are several types of backflow preventers available, each designed to address specific backflow risks. The correct choice of backflow prevention device will depend on the degree of hazard the system poses.

Air Gap: This is the most reliable backflow preventer. An air gap is a physical separation between the water supply outlet and the receiving vessel.

Reduced Pressure Principle Assembly (RPZ): This device is used for high-hazard applications. It features two independent check valves with a pressure-monitored chamber between them.

Double Check Valve Assembly (DCV): This device consists of two check valves assembled in series. It's used for medium hazard situations.

Pressure Vacuum Breaker (PVB): A PVB contains a loaded check valve that closes when the flow of water stops, and an air relief valve that opens when the pressure drops below atmospheric pressure.

Atmospheric Vacuum Breaker (AVB): This is a simple and cost-effective means of backflow prevention, ideal for situations where back-siphonage is the only risk.

Recommended Products

Zurn Wilkins

Recommended Products

Zurn Wilkins
No items found.

L B White Promise

When you're looking for top Wellington Plumbers, L B White is the company you can trust. We provide quality, reliable, and efficient plumbing maintenance services throughout the Wellington region. Our team of experienced professionals is dedicated to ensuring that your plumbing systems remain in top shape, saving you from future unexpected repair costs. Reach out to us today to schedule a maintenance consultation or to learn more about our services.

Send a Message

Thank you! Your submission has been received!
Oops! Something went wrong while submitting the form.

Get in Contact
04 587 1023
Mon to Fri 7:30AM - 5:00PM
42 Victoria Street, Alicetown, Lower Hutt