Guidance to determine water supply population

Supplies with a stable population base of less than 50 people.

As these suppliers generally know who is supplied at each connection, the population can be determined by identifying the total number of people ordinarily living at each address supplied per connection.

Supplies with a stable population base of 50 to 500 people.

Census mesh block population data is the preferred method if this method can be reliably used (refer to Large urban supplies below). Mesh block data is not always reliable for estimating rural populations as residents are often not connected to the drinking water supply.

An alternative method of estimating the drinking water supply population is to obtain the number of household connections associated with a supply and multiply by the average number of people per household (where the average number of household occupants is determined by Census data relevant to the supply or to the appropriate mesh block).

What is a mesh block?

Mesh blocks are the smallest geographic unit for which statistical data is collected in the census of New Zealand. It is a defined area, varying in size from part of a city block to large areas of rural land. There are online tools that allow the mesh blocks that relate to a particular drinking water supply to be summed to provide an estimate of the population serviced.

Supplies with a stable population base of more than 500 people.

The method of determining the water supply population commonly used by existing large water suppliers is to use the Geographic Information System’s mesh blocks published by Stats New Zealand to estimate the population supplied.

As these large drinking water supplies typically encompass large numbers of complete mesh blocks, determining their supply population can be relatively straightforward with some sense checking (Note: Exclude mesh blocks where only a small percentage of the population are served by the supply).

Supplies where for most of the time there is a stable base population but at certain times the population increases significantly.

An example of a varying population size is a small community with holiday homes where the population grows substantially over the holiday season.

The base population can be determined using, for the period of the stable base population, the methods for categories one to three above. For example:

• If urban community with small proportion of houses occupied, use category one’s method for the base population as the Census is conducted outside of when the population has increased; or
• If community is small, use category two or three’s method to determine the base population.

Estimating the increase in population can be determined by using, for the period of higher occupation, the number of connections multiplied by an occupancy rate (where the occupancy rate can be determined from bookings at accommodation providers such as holiday parks, camping grounds, hotels or motels, or indirect measure such as additional mobile phone connections or increase in water usage).

Total increased supply population is the sum of base population + increase in population estimate.

This method records both the stable population count and the total increased supply population.

Supplies which normally have no normal population or a very low population, (up to five people) and where events held at a place supplied by the water supply cause an influx of people and increase demand on the supply for a limited amount of time.

For example, events held at a marae such as hui or tangi, or events at a community hall.

Some of these supplies have no resident population, while others have a normal resident population. The following approach can be used to estimate the water supply population. Estimate the maximum number of visitors for a single event.

The total population is the sum of base population + the maximum number of visitors at a single event.

This situation covers short term events where people gather and where a drinking water supply is required for the duration of an event which continues for a limited time.

For example, events like music festivals, farm field days, civil defence, or military exercises.

The population can be determined by the total number of people attending the event from ticketing numbers or other attendance information.

Planned event temporary drinking water supplies are supplies that are established for a specific purpose and for a limited time. They are not emergency supplies which are dealt with differently under the Water Services Act 2021.

Supplies that provide water from a single site to a community who collect the water in containers.

An example of this is a tap that is not connected to a networked drinking water supply, which the public can use to collect drinking water in containers.

The population for a community drinking water station can be calculated or estimated:

• Where the number of people accessing the facility is known, use the maximum number of people that access the facility per day.
• Where the number of people accessing the facility is not known, estimate the population based on the volume supplied (where the population is calculated based on 2 litres per person, per day).

Please note: public taps or container filling stations that are connected to a network supply (e.g. community taps that provide water which is chlorinated and then de-chlorinated) are not considered to be community drinking water stations.

This covers the situation where water is provided to a single building. This does not include supply solely to a stand-alone domestic dwelling.

Where the self-supply has a normally resident population (e.g. papakāinga), the resident population should be used.

Where the self-supply is a workplace, the number of employees that work on site (i.e. industrial parks, ports) should be used.

Where the water supply is a commercial premise (such as a café), use the maximum number of customers and workers per day.

Where the water supply is a commercial premise (such as a hospital or aged care facility where it is both residents and workers), use the maximum number the combined population of residents and workers per day.

This covers the situation where water that is supplied from a vehicle with a water tank (e.g. a truck, trailer, or rail wagon), often to a storage tank on a property.

Typically, Water Carrier Services provide potable water to houses that have their own supply but need the quantity of stored water to be augmented. Water Carrier Services can also augment other water supplies particularly during droughts and emergencies and provide water to temporary planned events.

The population estimate is the number of times water is delivered for drinking over the previous 12 months (not the population they supply).