A summary of the concerns is set out below for each water body.
For a more detailed explanation of the concerns set out in the sections below, please view or download the report provided by our technical advisors which you can find at this link. The document will open in a separate browser tab with the same heading numbers as used below on this summary web page.
A. Reservoir & Downstream Concerns
It does acknowledge for the first time that discharging recycled effluent into the reservoir will cause algal blooms, which they admit would reduce biodiversity, and as a result they now plan to add a phosphate removal process, which will have to operate daily resulting in significantly increased costs, energy and carbon use. It is likely this new treatment plant will be located at the Water Recycling Plant site at Broadmarsh.
It is not credible for the report to conclude that there are no potential environmental effects from storing recycled effluent in the reservoir, other than the likely change in trophic state to eutrophic due to phosphorus, as there will be other effects from the discharge of recycled effluent into the reservoir. A summary of the concerns is set out below.
- Most of the contaminants of concern have NOT been considered, including contaminants found in the output water from the effluent recycling trial plant which operated at Budds Farm Sewage Works for a short period in 2023, such as pharmaceuticals, forever chemicals (PFAS), pesticides and volatile organic compounds (VOC).
- Inadequate consideration of risk of treatment chemicals and disinfection by-products being discharged into the reservoir and their potential impact.
- Loss of a unique biodiversity opportunity to create a chalk spring fed reservoir. Changes in geochemistry will have an adverse impact on the flora and fauna in the reservoir.
- A significant reduction in tropic status to eutrophic is identified because of the presence of orthophosphate in the recycled effluent discharge, giving an increased risk of algal blooms and an associated impact on biodiversity which is not acceptable.
- The additional treatment proposed to remove phosphate will not be guaranteed to maintain water quality to that of the original spring fed reservoir and prevent algal blooms.
- Additional cost and carbon impact due to the need for daily phosphate treatment of the recycled effluent and the operation of the bubbler/ aeration system in the reservoir from April to August each year to improve mixing, this is necessary because of the deterioration in water quality that will result from the discharge of recycled effluent.
- Additional sludge will be generated by phosphate treatment.
- The impact of a potential deterioration in water quality for ALL contaminants must be considered, it is not acceptable to only consider a small number of parameters for which there is an existing water quality threshold, as is currently the case.
- The impact of salinity and temperature changes in the reservoir and downstream are not adequately considered
- There is no assessment of the impact of effluent recycling on water quality in the wetland and in the reservoir shallows, the areas which will be of most importance for biodiversity.
- Concern regarding increased risk of blue green algae.
- The increased risk of pollution to the reservoir is not adequately considered. It is not good enough for Southern Water to say it won’t happen given their poor track record on pollution incidents and maintenance failures. Given the confined nature of the reservoir water body the impact of pollution incidents must be assessed, especially as there was no previous risk of this nature to the spring fed reservoir.
- Inadequate recognition of the downstream benefits the original reservoir provided.
- Impact of seasonal variation in downstream flow not adequately considered.
- No assessment of the potential impact on the stream to the south-east of the reservoir.
- Some of the baseline data and modelled outputs appear to be suspect when compared to previous independent modelling reports, with less parameters / contaminants modelled in 2025 than in previous studies.
- Inadequate assessment of the risks arising from the sewer catchment.
- Inlet position in the reservoir has changed and as a result the modelling is out of date.
- There is a lack of information on the inputs and assumptions being used to model and assess the impact of effluent recycling on both the spring fed reservoir and downstream water courses (level of mixing, data being used for the recycled effluent discharge etc.). Multiple operating scenarios need to be modelled to assess the impact, along with further sensitivity analysis to determine the effect of changes in the inputs and operating scenarios.
- Not clear who has undertaken the water quality modelling/ assessment. Is it a completely independent study? If not, it is unlikely that the community will accept the findings.
B – Langstone Harbour Concerns
The changes in water quality and associated impacts to Langstone Harbour have NOT been adequately assessed, nor have the risks. A summary of the concerns is set out below.
- There will be a reduced nitrate benefit to Langstone Harbour if effluent recycling goes ahead, this has not been considered. The benefit was confirmed by water quality modelling for the spring fed reservoir in 2011 and 2020.
- The risk of contaminants from the reject water discharge into the Solent reaching Langstone Harbour has been dismissed. The time period over which the discharge has been modelled is not clear and may not have been long enough to assess the true extent of the effects of discharging more concentrated reject water in to the Solent. Previous modelling of the existing long sea outfall discharge has shown that multiple tidal cycles can carry the plume from the outfall a large distance stretching from the entrance to Southampton Water and along the coast to Bracklesham Bay, with parts of the plume modelled entering the harbours.
- Day-on-day cumulative and in-combination impacts of effluent recycling are not adequately considered for Langstone and Chichester Harbour.
- Risk to Langstone Harbour of building the Water Recycling Plant on the Broadmarsh dilute and disperse landfill is not considered.
- Risk to the harbour from future effluent recycling pipeline construction (including blow-outs), maintenance or bursts are not considered.
C – Solent Modelling Concerns
The report concludes that there will be no likely significant effects in the Solent but there is insufficient information to draw this conclusion. The reject water from the effluent recycling plant will contain thousands of contaminants of potential concern to the Solent. As a result, there is the potential for significant adverse effects on the marine environment and additional more comprehensive work on marine dispersion modelling and outputs is required to clarify the risks under different operating scenarios.
Specific concerns include.
- Most of the contaminants of concern have NOT been considered including pharmaceuticals and many forever chemicals which can be persistent in the environment.
- There will be additional new contaminants of concern in the reject water from the effluent recycling plant including treatment chemicals, cleaning chemicals and treatment by-products which must be properly considered. The risk that these extra contaminants pose to the marine environment has not been adequately considered.
- The forecast decrease in predicted concentration of all 7 contaminants considered in the modelling is highly suspect. That makes no sense when the reject water will be 3 or 4 times more concentrated than the existing LSO discharge.
- The impact of changes in salinity and temperature are not adequately considered.
- No consideration of the risks/ impacts of bioaccumulation or from sedimentation. Research by Portsmouth University has shown that contaminants found in sewage can accumulate in algae. Algae are eaten by other species and can settle on the sea bed when they die.
- It is not clear what the cumulative effects on the Solent of day-on-day discharge of more concentrated reject water will be, or how this is to be assessed.
- Concerned about what the in-combination effect on the Solent of day-on-day discharge of effluent from multiple long sea outfalls will be, including the 3 planned effluent recycling plants (Havant, Littlehampton & Sandown). This has not been considered.
- No information on what happens to the sludge from the effluent recycling plant, where this will be discharged? – Will it be to the Solent? How and when will the impacts of this be assessed? More sludge will be generated as a result of the proposed additional phosphate treatment.
- There is a lack of information on the inputs and assumptions being used to model and assess the impact on the Solent (volumes, level of mixing, data being used for the reject water discharge etc.)
D. New Surface Water Drainage System Concerns
The new drainage system will be located on top of, or within, an uncontained landfill site that contains toxic and mobile contaminants (leachate). The additional risks the developed site poses to water quality have not been adequately assessed.
A summary of the concerns is set out below.
- Increased risk of pollution from chemicals and sewage effluent stored and processed at the Water Recycling Plant site. Given Southern Water’s poor track record on maintenance (fix on fail) and pollution incidents during maintenance this is a significant concern. It is certainly not acceptable to assume that there is no pollution risk, as is currently the case.
- Increased risk of leachate pollution to the stream/ harbour via the new surface water collection features/ pipe. This could arise as a result of settlement in the landfill disrupting the new drainage features (or bedding materials), as a result of poor maintenance, or during construction and maintenance of the drainage system.
- Lack of detail available to assess the surface water modelled outputs
Even if a water quality risk is outside of the scope of the existing report it is still a risk to the water environment and it should at least be acknowledged.
Havant Matters 