Water neutrality in Sussex North and its legal basis

Water neutrality in Sussex North means that total water use in the supply zone must be no higher after a development is built than it was before. It is not a local policy choice. It follows from the duty on a competent authority under the Conservation of Habitats and Species Regulations 2017, because abstraction serving the zone draws on groundwater connected to the Arun Valley designated sites, and the authority cannot grant permission for a project likely to have an adverse effect on the integrity of those sites.

As at October 2026 the constraint remains in place and the practical requirements are set by the authorities within the zone. Confirm the current position with the local planning authority and the water undertaker before pricing a scheme, because the offsetting arrangements have changed more than once.

Why the constraint arose

Natural England issued advice in September 2021 about water abstraction in the Sussex North water supply zone and its effect on protected sites in the Arun Valley. The zone covers parts of north West Sussex, falling within the Horsham, Crawley and Chichester areas, and the practical effect was that applications for development generating new water demand stalled across a large area.

The designated sites in the Arun Valley are classified as a Special Area of Conservation, a Special Protection Area and a Ramsar site. Their qualifying features include wetland habitats dependent on groundwater levels, and species sensitive to changes in those levels.

The concern is not water scarcity in the ordinary sense. It is that increased abstraction to serve new homes could lower groundwater and change the hydrology of a site whose features depend on it. Once that possibility is identified, the habitats duty takes over.

The habitats duty that produced it

Regulation 63 of the Conservation of Habitats and Species Regulations 2017 requires a competent authority, before granting permission for a plan or project likely to have a significant effect on a European site, to make an appropriate assessment of the implications for the site in view of its conservation objectives.

The authority may agree to the project only if it can establish that there will be no adverse effect on the integrity of the site. The standard applied by the courts is demanding: the authority must be able to reach that conclusion with no reasonable scientific doubt remaining.

Where it cannot, the only route is the derogation for imperative reasons of overriding public interest, with compensatory measures and, for sites hosting priority habitats or species, further restrictions. That route is rarely realistic for housing.

Water neutrality is therefore a way of removing the effect rather than justifying it. A scheme that adds no net demand to the zone does not increase abstraction, so the appropriate assessment can conclude there is no adverse effect.

This is the same legal machinery that produces nutrient neutrality in other catchments, applied to a different pathway. Do not treat guidance on one as guidance on the other.

What water neutrality requires of a scheme

The standard definition is that water use in the supply area before the development is the same or lower after it is in place. Delivering that has three parts, and they run in order.

1. Reduce demand within the development itself, as far as the design and the Building Regulations allow.
2. Offset the remaining demand by reducing consumption elsewhere in the same supply zone, by a verifiable amount, secured for a period that matches the lifetime of the development.
3. Monitor and report, so that the assumed savings can be checked against what actually happens.

Each step needs evidence rather than assertion. An application that states a litres per person per day figure without a fittings schedule, and offers an offsetting contribution without identifying what the money will buy, will not get an appropriate assessment past the authority's ecologist.

A Water Supply Assessment setting out the demand calculation, the fittings specification and the offsetting mechanism is the document that carries this, and the calculation has to be auditable line by line.

Offsetting measures and their evidence

Offsetting works by retrofitting water efficiency into existing buildings in the zone, so that the saving achieved there is at least equal to the new demand created.

The measures used are unglamorous and effective: replacing cisterns and fittings in existing homes, fixing leaking supply pipes, installing meters where premises are unmetered, and retrofitting commercial and institutional buildings where consumption per building is high.

Three evidential questions decide whether an offset is accepted.

Is the saving additional. A measure the water company would have delivered anyway through its own programme does not count, because the baseline already includes it.

Is the saving secured for long enough. A fitting replaced today can be replaced with a less efficient one in ten years, so the mechanism has to address durability and replacement.

Is the saving measured or modelled. Metered before and after data is far stronger than a manufacturer's figure applied to an assumed occupancy.

Where offsetting is delivered through a payment to a scheme, the application needs to show what the payment buys and who is contractually obliged to deliver it.

Fittings specifications and their limits

Building Regulations set a water efficiency requirement for new dwellings, with a tighter optional requirement of 110 litres per person per day that planning authorities can apply through policy. Water neutrality typically requires designs well below that optional figure.

The fittings-based approach calculates demand from the specification of each outlet: the flow rate of taps and showers, the flush volume of WCs, the capacity of baths, and the water consumption per cycle of white goods where these are provided. Reducing the figure is a matter of specifying low flow showers, dual flush cisterns at low volumes, aerated taps and smaller baths.

The limits are real. Below a certain point the design becomes unattractive to occupiers, and fittings can be changed the week after completion. Rainwater harvesting and greywater recycling reduce mains demand further and bring maintenance obligations, commissioning requirements and a management burden that someone has to carry for the life of the building.

For non-residential schemes the arithmetic differs entirely, because process water, cooling and irrigation can dominate. Treat landscape irrigation as a demand to be designed out, which also helps the surface water case set out in a Drainage Strategy.

Strategic mitigation and its availability

The efficient answer to a zone-wide constraint is a zone-wide offsetting scheme that developers can buy into, rather than each applicant assembling its own retrofit programme.

Arrangements of that kind have been developed, and availability and price have varied. For a developer the practical questions are whether capacity exists now, how it is reserved, what the unit cost is, and what happens to the reservation if the scheme is delayed.

Build the answer into the programme. Where capacity has to be secured before an appropriate assessment can conclude favourably, the offsetting agreement sits on the critical path alongside the planning application itself.

Smaller schemes face a proportionality problem. The transaction cost of bespoke offsetting falls hardest on a single plot or a handful of units, which is why a pooled scheme matters most at that end of the market.

Checking the current position with the authority

Do this before anything else on a site in the area.

• Confirm with the water undertaker whether the site lies within the Sussex North water supply zone, by address rather than by assumption.
• Ask the local planning authority for its current requirement, including the demand figure it expects, the form of calculation and the offsetting route it will accept.
• Ask what evidence the authority's appropriate assessment will need, and whether a draft can be reviewed before submission.
• Check whether the position has moved. Regulator advice in this area is updated, and an application prepared against last year's requirements may be refused on the current ones.
• Keep a dated record of every answer, because the file is what supports the assessment.

Habitats constraints of this kind interact with other ecological duties on a site, and the exceptions within the biodiversity regime work differently again, as irreplaceable habitats and the biodiversity gain exception sets out. The PlanScope planning law timeline is a place to follow changes of this kind.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it, and obtain specialist hydrological and ecological advice for any habitats assessment.

For specialist technical reports, qualified professional input may be required. Enter the site postcode on PlanScope to see which documents a scheme in a constrained catchment is likely to need. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.