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Feasibility and technical reports: summary

Updated 13 June 2024

Applies to England

The Department of Health and Social Care (DHSC) commissioned feasibility and technical reports from Northumbrian Water Limited (NWL) as part of identifying an operable and efficient scheme for this proposal. A summary of these reports is below.

Further information is available on request by emailing waterfluoridationconsultation@dhsc.gov.uk.

Feasibility study

The study was carried out under the following conditions:

• the fluoridated water will be supplied at a concentration of no less than 1 part per million (ppm)
• those areas of the water distribution system which will receive fluoridated water with concentrations less than 1.0 milligrams per litre (mg/L) due to mixing of unfluoridated water sources will be identified
• identify the most practicable method of fluoridating the greatest area within the water network with each fluoridation plant
• identify the various options which are available to achieve this outcome and recommend the most cost effective, safe and resilient way to achieve this, based upon an assessment of all the reasonable options

Based on the above conditions the most efficient and least cost option would be to install fluoridation plants at all the major water treatment works within NWL’s northern area of supply. This will ensure that the maximum number of customers are supplied from a single fluoridation plant.

If the above procedures are adopted there will be, however, isolated rural areas where it will be impractical due to their physical location to supply these areas with fluoridated water. The physical practicalities of supplying small, localised areas with fluoridated water will involve a large investment in water mains infrastructure for around 0.04% of the total potential population.

The cost per person for supplying fluoridated water to small areas with a low population will be far greater than that of supplying fluoridated water to large areas with a high population. The requirements for additional water mains infrastructure and fluoridation plant costs for small rural populations can, if required, be assessed later.

Water supply

In the main there are 3 types of water supply:

• impounding reservoirs
• river abstraction sites
• borehole supplies

All these types of supply are used by NWL in the north east of England.

Impounding reservoirs

These are artificial and sometimes natural lakes that collect rainwater prior to it being supplied to water treatment works.

River abstraction

Rainwater falls on hillsides and then runs into streams and rivers. These waterways are then used as a method of bulk water transportation across large distances from a rural source to an urban destination without the need to have water mains infrastructure. River water can then be pumped directly to an urban water treatment works.

Borehole supply

Rainwater percolates through soil layers and can then pass into and be stored in materials like sand, clay, gravel or limestone. These storage units are called aquifers or water-bearing strata. Boreholes can be drilled down to reach these aquifers and water can then be abstracted from them. Because this water has been filtered while passing through the aquifer, all that needs to be added to the water is chlorine to provide a potable drinking water source.

Water treatment works

Generally, chemical additives are used in the water treatment process to remove colloidal particles and to kill certain bacteria and other microbes. At some water treatments works fluoride is added. Consequently, when fluoride is added at the water treatment stage, all customers supplied from that water treatment works are provided with fluoridated water.

If fluoride is not added at a water treatment works, then any area downstream of the works requiring fluoridated water will need an individual fluoridation plant.

Water distribution

In the UK, water supply was originally carried out by hundreds of small local water boards. These companies were established some 2 centuries ago and since then have gradually been amalgamated. Currently, there are 25 water companies covering England, Scotland and Wales.

Consequently, the configuration of most water distribution systems has developed over time and evolved almost organically as water systems have merged and additional population centres have expanded the network.

Water distribution systems, to a great extent, tend to have some form of water treatment at the head of the system and a downstream network that contains principal trunk mains that branch out into smaller diameter distribution mains. These in turn feed local mains that then supply individual households and commercial premises. Water companies also compartmentalise sections of the distribution network to allow water accounting to take place and to help in leakage location.

In general, the area supplied by a water treatment works is called a system zone. These zones are areas that are hydraulically isolated from other parts of the distribution network and can contain 40,000 to 80,000 properties. The system zones are then subdivided into district metered areas that are hydraulically isolated units that contain 500 to 2,000 properties.

As a result of the merger of separate small water boards, and the design of water distribution systems and the creation of system zones and district metered areas, it is not uncommon for a population centre to be supplied from several different sources. In some cases, the water mains network within such population centres will be unconnected, with each individual source supplying a separate area.

This generalised structure of water distribution with a water treatment works at the head of the system supplying large population areas lends itself to mass fluoridation with a fluoridation plant at every major water treatment works.

Northumbrian Water’s area of supply

NWL’s northern area of supply covers the counties of:

• Northumberland
• Durham
• Tyne and Wear
• Teesside

The northern area supplies 2.5 million customers. The company has 3 separate areas within its northern sphere of operation each one supplying water to customers. These areas are: the North, Central and Tees.

The southern area of supply covers the counties of Essex and Suffolk. This report does not cover the southern area of supply.

The boundaries of the supply areas do not conform with those of the county boundaries. This is due to the original areas covered by the old water boards and the fact that water supply sources follow the topographical nature of the landscape.

NWL does not supply the Borough of Hartlepool. This area is supplied by Anglian Water.

Fluoridation plant installation

This part of the feasibility study deals with the configuration of the water distribution network within NWL’s northern area of supply.

It does not identify where within the grounds of a water treatment works the fluoridation plant should be located. To enable this information to be identified, site visits must be made to each water treatment works to ensure that there is the capacity to install a fluoridation plant at the works. It may also be necessary, once the location of the fluoridation plant is identified, to ensure there is a common point of dosage and the capacity to install additional mains infrastructure. This will almost certainly occur at those water treatment works where multiple trunk mains leave the site. The fluoridation plant must therefore be capable of supplying fluoride to multiple outlet mains.

Technical study

At present, NWL undertakes fluoride dosing at a number of sites, although the coverage in terms of population served is not 100%.

In general, the options to facilitate supply of fluoridated water to 100% of the population in NWL’s area of supply require the installation of fluoride dosing systems at additional water treatment works, although there is a background concentration of natural fluoride at some sites.

A set of engineering risks have been identified with implementation of all the fluoride schemes. Fluoride dosing is predicted to increase the number of properties which may be exposed to fluorapatite (a crystalline compound) formation risk, and requires further investigation through subsequent implementation. Also, the way fluoride dosing is controlled in groundwater stations would need further definition and agreement.

Target fluoride concentration

DHSC has indicated that a fluoride concentration range of 0.8 mg/L to 1.2 mg/L will be acceptable, but below 0.8 mg/L would compromise dental health. In each case the written agreement will specify the actual target concentration.

The DWI ‘Code of Practice on Technical Aspects of Fluoridation of Water Supplies 2021’ (on the DWI Guidance and codes of practice page) sets a ‘normal’ target fluoride concentration of 1.0 mg/L for a fluoridation scheme. The maximum prescribed concentration and value (PCV) for fluoride under The Water Supply (Water Quality) Regulations (2016) is 1.5 mg/L as measured at customers’ taps.

General approach and assumptions in technical report

The new schemes have been based on the following:

• at the target fluoride dose of 1.0 mg/L when applied at the water treatment works
• design to comply with the ‘DWI Code of Practice on Fluoridation of Water Supplies 2021’

Risks identified

Fluorapatite formation

Fluorapatite crystals are hard and highly insoluble within the normal range of potable waters. Formation of the compound is accelerated by an increase in temperature. In some circumstances there is a risk of problems resulting from scale formation in domestic boilers.

In 2007, UK Water Industry Research Ltd proposed a model, based on water quality parameters, which could be used to provide guidance of fluorapatite risk (see Investigation into the emerging issue of fluorapatite formation). Modelling indicates that:

• presently there are no domestic properties in the ‘high risk’ category for fluorapatite formation, and this picture does not change with implementation of the new fluoride schemes
• implementation of the fluoride dosing schemes will increase the number of domestic properties in the medium risk category from 0 to 287,000 (18% of the overall number of properties)
• potentially, a total of 5,840 wholesale customers could be affected by fluorapatite

Further work should include sensitivity analysis and the evaluation to consider the seasonality of water quality parameters. In terms of risk response to fluorapatite, a strategy to address the risk should:

• consider holistic water quality needs
• not be carried out in isolation from other water quality strategies
• be revisited depending on the parameters driving fluorapatite risk

Environmental

In terms of installation of the fluoride dosing systems themselves, no environmental screening has been undertaken. As the proposals would be located within the existing site boundaries, it is assumed that the environmental and third-party risks are low. However, it is recommended that environmental screening is undertaken at the next stage of design.

Fluoride at a concentration of 1 mg/L may be present in water discharged from the site as part of any planned or unplanned activities, typically where water needs to be disposed of. The risk of specific discharge constraints with respect to fluoride is low. However, it is recommended this is confirmed with the Environment Agency at the next stage of the project.

Asset degradation

Fluoride may contribute to the deterioration of the concrete lining of pipes in the water supply network. This may incur additional costs. We would recommend that this risk is examined at the next stage.

Design and costing

To further understand the costs and risks for each site, further design work is required. There is a general risk that engineering capital costs may increase after further site investigation and design has been carried out.

Requirement for pH correction dosing

There is a low risk that the introduction of fluoride will cause a change in water chemistry at the treatment works requiring an adjustment to pH. However, this requires confirmation with NWL water quality stakeholders.

Opportunities

There are appreciable levels of natural background fluoride. Careful management of blending water supplies may offer an alternative to introducing other more costly dosing infrastructure.

There is an opportunity to work with the supply chain to develop standards that could improve efficiency of delivery in terms of costs and programme.

Conclusions

NWL has identified that fluoridation may be required at water treatment works to achieve the goal of 100% fluoridation in their supply area.

Some sites have sufficient background concentration and will not require fluoridation. A further site will blend with another source to be fluoridated and will not require fluoridation.

A set of risks have been identified as described in the feasibility reports with implementation of all the fluoride schemes. Fluoride dosing is predicted to increase the number of properties supplied which may be exposed to fluorapatite formation risk, and this requires further investigation.

Lastly, the way fluoride dosing is controlled in groundwater treatment works needs further definition and agreement with NWL.