Water neutrality in Sussex North and the evidence needed

Water neutrality in Sussex North means a development must not increase the total amount of water taken from the Sussex North water supply zone, so any demand the new homes create has to be matched by savings made somewhere else in the same zone. Planning for water neutrality sussex north therefore needs two pieces of evidence: a calculation of the scheme's demand at a stated efficiency standard, and a deliverable, secured offsetting package that cancels it out.

It is not a flood risk issue and it is not nutrient neutrality. The mechanism is different and so is the arithmetic.

How the position arose

Natural England advised that abstraction serving the Sussex North water supply zone could be affecting the internationally designated wetland habitats of the Arun Valley, which are protected as a Special Area of Conservation, a Special Protection Area and a Ramsar site. Under the Conservation of Habitats and Species Regulations 2017, a local planning authority as competent authority cannot grant permission for a project likely to have a significant effect on such a site unless an appropriate assessment shows no adverse effect on integrity, alone or in combination with other plans and projects.

Because the effect arises from the cumulative demand of new development on a constrained supply, the way through is to show that the development adds nothing to that demand. Hence neutrality.

The affected authorities and the water company have produced joint strategy work on how neutrality can be achieved. Read the current version on the councils' own websites rather than relying on an older summary, because the offsetting mechanisms and the standards have moved since the advice was first issued.

The zone and its boundary

The constraint follows the water supply zone, not a council boundary. Parts of the affected districts sit inside it and parts do not, and a site on the edge needs the position confirmed rather than assumed.

Two checks, in this order:

1. Ask the water undertaker to confirm in writing whether the site is within the Sussex North water resource zone and which source serves it.
2. Ask the local planning authority to confirm its current position on the constraint and what it expects to see with an application.

Do both before you buy. A site inside the zone with no realistic offsetting route is worth a different number from the same site outside it.

What neutrality means arithmetically

Neutrality compares the water used before the development with the water used after it, across the zone.

For a greenfield site the before figure is effectively zero, so the whole of the new demand has to be offset. For a redevelopment the existing lawful use may have a measurable consumption that can be credited, provided it is evidenced from metered records rather than estimated. That credit is the single most valuable thing a brownfield site in the zone has.

The demand side is calculated from the number of bedrooms, an occupancy assumption and a litres per person per day figure. Part G of the Building Regulations sets a water efficiency requirement for new dwellings, with a tighter optional requirement of 110 litres per person per day that applies where a planning condition imposes it. Water neutrality work in this area pushes below that optional requirement, with the residual demand offset. Check the figure the authority is currently applying, because it is set by local strategy rather than by national regulation.

Worked illustration, and the numbers here are illustrative only. A scheme of 12 three bedroom houses at an assumed 2.6 people per dwelling and 85 litres per person per day produces a demand of roughly 2,650 litres a day. If the site previously held a building with metered consumption of 400 litres a day, the shortfall to offset is about 2,250 litres a day. The offsetting package then has to deliver that saving for as long as the development exists.

Water efficiency in the new homes

Fittings first, because every litre saved in the design is a litre you do not have to buy back.

The usual specification runs to low flow taps and showers, dual flush or low volume cisterns, water efficient white goods where the developer supplies them, and flow restrictors. Rainwater harvesting and greywater recycling reduce mains demand further, and some authorities will count them, though they bring maintenance obligations that need to survive the sale of the house.

Set out the fittings schedule as part of the application, not as a reserved matter. An Energy Statement often sits alongside it, and the two documents share the same specification appendix, which saves repeating the schedule in two places.

Expect a condition requiring the dwellings to be built to the stated standard and a mechanism for demonstrating it before occupation.

Offsetting and how it gets evidenced

Offsetting means reducing existing demand in the same zone. The routes in use include retrofitting water efficient fittings in existing homes, in social housing stock or in public buildings, and in some cases leakage reduction or the decommissioning of an existing supply.

What an authority needs to see:

• the quantified saving per measure, with the source of the figure
• the number of properties or assets to be treated, with named or categorised recipients
• who delivers the works and who pays
• a monitoring and reporting regime
• how the saving is secured for the lifetime of the development

That last point is where schemes fail. A retrofit done once in year one does not obviously persist for 80 years, so the strategy has to deal with replacement cycles and with the behaviour of occupants. Authorities have been conservative about accepting savings they cannot verify, and reasonably so.

Where a credit scheme operated by the authority or by a third party is available, buying into it is usually faster than assembling a bespoke package. Where it is not, the applicant does the work.

Securing the measures

A planning condition can require the dwellings to achieve the efficiency standard. It cannot easily require works to third party land, so the offsetting package is normally secured by a section 106 obligation, with a payment or a works schedule, a delivery timetable and reporting duties.

Draft the obligation so that the saving is in place before occupation rather than afterwards. Phased schemes need the offsetting phased to match, which is awkward and needs to be modelled at the outset.

The interaction with the appropriate assessment is the thing to keep in view. The authority has to be able to conclude no adverse effect on integrity, and it can only do that if the offsetting is certain at the point of decision. Uncertainty in the mechanism becomes uncertainty in the assessment, and the application stalls.

Our note on groundwater abstraction points and the 50 metre rule covers the separate source protection issue, and the weight question for an allocated site inside a constrained zone is discussed in our piece on local plan site allocations and their weight.

For specialist technical reports, qualified professional input may be required.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.

Browse all 66 PlanScope report types to see which documents a scheme inside a water neutrality area needs: start at the report index.

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