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Backflow prevention

What is backflow, and how does it happen?

We’re all used to water coming out of a tap when we turn it on. A backflow situation is the opposite of this. When backflow occurs, it can suck water back into a system like a vacuum or water can be forced back into the system when the pressure downstream of an outlet is greater than the pressure in the water main.

Learn more:Seven Sharp celebrates International Backflow Prevention Day | TVNZ On Demand

Types of backflow:

Back-Siphonage: This is caused when there is a negative pressure situation in the water supply pipe. This can cause the supply pipe to act as a vacuum.

If you’ve ever changed a tap washer and heard a gurgling sound while you’re working on it, this is an example of siphonage occurring.

Back Pressure: This happens when the downstream pressure in a property’s water supply is higher than the supply pipe pressure. With no means to stop it, this higher pressure overrides the water in the supply pipe and causes the water to flow backwards.

An example of this occurring would be a heated boiler system directly connected to a water supply. As the water is heated, the pressure increases and with that its ability to overcome the lower pressure cold water in the supply pipe.

Boundary Backflow Prevention

Backflow into our public water supply is one of the biggest risks we face in terms of drinking water safety. If it occurs, it can seriously compromise the quality and safety of our drinking water. The water in our pipes moves around the city at speed, and so a contamination at one point can easily spread from the initial source. Following the 2016 water supply contamination event in Havelock North, the Government set about making a raft of legislative changes to better protect public water supplies and maintain public health.

What does the law require?

Two main pieces of legislation have been introduced – the Water Services Act 2021 and the Drinking Water Quality Assurance Rules 2022. The Government’s water regulator, Taumata Arowai, oversees this legislation and ensures that water suppliers are complying with it. Under this legislation, Invercargill City Council is a water supplier.

Section 27 of the Water Services Act 2021 requires drinking water suppliers to ensure that their supply arrangements protect against the risk of backflow.

Section 4.11.1 D3 of the Drinking Water Quality Assurance Rules 2022 contains the backflow prevention rules that Invercargill City Council is required to comply with. Six key rules require water suppliers to:

  1. Prepare and implement a backflow prevention programme to protect their distribution system against the risk of backflow.
  2. Conduct periodic surveys of backflow risks to the distribution system to determine medium and high-risk sites in order to assess the adequacy of backflow prevention across the distribution system. This must be done at least once every five years.
  3. Where backflow requirements at the point of supply are deemed inadequate, Council must ensure a suitable backflow prevention device is fitted in a timeframe commensurate with the risk, but as soon as reasonably practicable.
  4. Ensure all boundary backflow prevention devices are tested at least annually.
  5. Maintain a location register of all point-of-supply testable backflow prevention devices, types, assessed risk level, and the annual test results.
  6. Restrict standpipe access to the water network (via hydrants) to only Fire and Emergency New Zealand (FENZ), other emergency services, Council staff or authorised contractors (where it is reasonably necessary to access the network for the operation of the drinking water supply).

How does Council comply with these new rules?

Council has updated their existing Water Supply bylaw to reference the new legislation and created a new backflow prevention policy, which can be found here. The bylaw gives effect to the policy, and the policy provides the rules and the details of what is required to comply with the backflow rules above.

What does the backflow prevention policy require?

In short, the policy requires backflow prevention devices to be fitted at the boundary of every property connected to the public water supply. The policy aims to cover all six of the rules that Taumata Arowai has developed.

The policy categorises properties into four risk hazard types based on the risk that each property poses to the public water supply.

The policy then specifies the minimum backflow prevention device that each hazard requires.

The different responsibilities that the customer and Council have, and the difference in ownership arrangements, are explained in the policy.

It clarifies that the cost of installation, maintenance and ongoing annual testing sits with the property served by that water supply.

It covers water supplies that are connected to fire suppression systems and the unique requirements that apply to these. It also restricts the use of fire hydrants in the street to only the likes of FENZ, emergency services, Council staff and authorised contractors.

Council’s proposed approach to having boundary backflow preventers fitted:

Council will be starting with all existing medium and high-risk properties first, as they pose the biggest risk to the water supply. Council will survey these properties, and where there are inadequate backflow prevention measures in place, it will require owners to have a suitable backflow prevention device installed and tested.

As new builds occur, these will be looked at irrespective of what risk hazard category they are and will require the appropriate boundary backflow prevention device to be fitted as part of their building consent.

As water connections are requested to be installed by Council outside of the above scenarios, these will be looked at on a case-by-case basis and may require the installation of backflow prevention at that time.

Lastly, Council will be looking at low and very low risk properties unless called upon to look at these earlier.

Testing and maintenance requirements:

In accordance with rule 4 noted above from the Drinking Water Quality Assurance Rules 2022, all testable boundary backflow prevention devices are required to be tested at least annually. The cost of this will sit with the property owners.

Where these sit inside the property boundary, the testing will be arranged by the owner and done as part of their building warrant of fitness. Where they sit outside the boundary, Council will arrange testing and pass on this cost to property owners.

Testing can only able to be carried out by someone approved under the Building Act 2004 as an independently qualified person.

Frequently asked questions:

A backflow prevention device is a valve installed on a water supply to prevent backflow from occurring. Its purpose is to protect the water supply.

There are four categories in the backflow prevention policy being high, medium, low and very low. These are defined as:

High:Any premises, condition, device or practice which, in connection with the potable water supply system, has the potential to cause death.

Medium: Any premises, condition, device or practice which, in connection with the potable water supply system, has the potential to injure or endanger health.

Low:Any premises, condition, device or practice which, in connection with the potable water supply system, would constitute a nuisance, by colour, odour or taste, but not injure or endanger health.

Very low:Properties that constitute a very low risk of contamination, but as they sit above the water reticulation, could allow water to return into the mains supply in the event of depressurisation of the network. Most households would fall into this category.

The risk categories determine the minimum level of backflow prevention device required based on the consequences if a backflow incident were to occur. Within the tables in the backflow prevention policy under each risk hazard category, there are examples of premises, conditions, devices and practices that align with the risk level. Where there is doubt or if a specific case or example does not feature in the tables, then comparison to the hazard descriptions must be made to determine what category it falls under.

Backflow preventers already installed are likely to be point-of-use devices installed to protect the internal water supply and users inside the property. These are required under the Building Act 2004. The ones we are requiring to be installed now are at the boundary and are for the protection of the public water supply.

It is Council’s preference to have property owners engage their own plumbing contractors where the backflow preventer can be located inside the property boundary. Where, in an existing situation, the building is hard up against the boundary and the backflow preventer needs to go outside the property on public land, then a Council-approved contractor will need to install this.

Backflow preventers are required to be tested at least annually. Testing is only able to be carried out by someone approved under the Building Act 2004 as an independently qualified person for backflow prevention devices.

Yes. The public water supply must be protected from backflow of any substance, regardless of whether that substance is considered non-toxic. While these substances may not pose immediate health risks, they can still alter the colour, odour, or taste of drinking water – a quality compromise that regulations strictly prohibit. There is also a risk of how these react with the additives to the water supply, which are used as part of the treatment process.

From a Council perspective, we do not differentiate between the property owner and the tenant when assessing the property. We are only looking at the risk each site poses, rather than who is responsible for this. As we do not hold records of tenants, rental agreements and leases, we will write to the property owner in the first instance. If you are a landlord and are concerned with tenancy changes affecting boundary backflow prevention requirements, we would encourage you to have this aspect covered in any agreements you have in place with your tenants.

Council will always look to work with property owners; however, if a required backflow prevention device is not installed in time and we’re not satisfied that it is going to be installed in an agreeable timeframe, we do have the ability to take action under the Council’s Water Supply Bylaw 2017. This may initially begin with restricting the water supply, through to having the backflow preventer installed by a Council contractor and charged to the owner.

For those backflow preventers required to be installed inside the boundary, yes, these require a building consent. As part of this process, the backflow preventer will be added to the existing compliance schedule for the site, or where there isn’t a compliance schedule in place, this will be the trigger to create one.

It is around the consequences of contamination occurring, not the frequency. Much like earthquakes, backflow events are unpredictable. If one does happen, the grid design of our water supply network means that in a short timeframe, the contamination could cover dozens of city blocks. With the high and medium risk sites, contamination from these can lead to serious public health issues.

The property owner is required to pay for the cost of the installation and maintenance of the backflow preventer and the annual testing. There are differences in how this is done between residential and industrial/commercial.

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