Water neutrality: what applicants have to show in affected areas
In affected water resource zones a scheme has to cut per person water demand and offset what is left, with the offset secured before permission can be granted.
Water neutrality means a development must not increase the rate of water abstraction from the environment above the level before it was built. In practice an applicant in an affected area has to do two things: design the homes to use markedly less water than the Building Regulations require, and offset whatever demand is left by reducing use somewhere else in the same water resource zone.
The requirement is not a design aspiration. It comes from the Conservation of Habitats and Species Regulations 2017, and where it applies the local planning authority cannot grant permission until it can conclude that there is no adverse effect on the integrity of the protected site.
Where the requirement bites
The best known case is the Sussex North water resource zone, where Natural England advised authorities that abstraction was affecting internationally designated wetland sites in the Arun Valley. Development across parts of Horsham, Crawley and Chichester has been assessed against water neutrality since that advice was issued in 2021.
Other water resource zones face pressure on abstraction, and the approach could be applied elsewhere where a designated site is affected. Check the position with the local planning authority and with the water undertaker before assuming a site is outside it, because the boundary follows the water resource zone rather than the district.
Like nutrient neutrality, water neutrality has no unit threshold. A single dwelling that increases demand is caught. Unlike nutrient neutrality, the pathway is abstraction rather than discharge, so the calculation and the mitigation are different exercises even where both regimes apply to the same site.
The three step approach
The strategies produced for affected areas follow the same order, and applicants are expected to work through them in sequence rather than jumping to the end.
- Reduce demand in the new development as far as design allows.
- Offset the residual demand by reducing existing demand within the same water resource zone.
- Consider new resources or other measures only where the first two cannot close the gap.
Step one is where the applicant has most control and where the evidence costs least to produce. Step two is where the programme risk sits, because an offset scheme needs a delivery mechanism, a legal agreement and often a third party willing to be retrofitted.
Designing the demand down
Building Regulations Part G sets a baseline of 125 litres per person per day for new dwellings, with an optional requirement of 110 litres per person per day that a planning condition can impose. Water neutrality areas expect a figure well below the optional requirement, and the target is set out in the relevant strategy or council position statement. Take the current figure from that document rather than from an earlier scheme.
Getting there uses a combination of measures, and the water calculator in the Part G methodology is how the figure is demonstrated:
- Low flow taps, showers and appliances specified by flow rate rather than by brand.
- Dual flush cisterns at the lower end of the available range, and no oversized baths.
- Rainwater harvesting for external use and, where the design allows, for toilet flushing.
- Greywater recycling on larger schemes, where the maintenance regime can be secured.
- Smart metering and leak detection, with the operational arrangements described.
- Landscape design that does not need irrigation in a dry summer.
Specify the flow rates in the submission. A statement that fittings will be water efficient is not capable of being conditioned or checked.
Non-residential development is assessed differently, usually on a per-employee or per-visitor basis, or through the water credits in an environmental assessment method. A BREEAM Pre-Assessment can carry that evidence where the scheme is pursuing certification, and a licensed assessor is needed for the formal assessment.
Offsetting the residual demand
Offsetting works by finding existing water use in the same zone and reducing it permanently. The usual mechanism is a retrofit programme: replacing fittings in existing housing, schools, leisure centres or commercial premises, and evidencing the saving.
Three practical constraints shape what is deliverable.
The saving has to be additional. Work the water undertaker was already going to do under its own efficiency programme does not count, because it would have happened anyway.
The saving has to last. A retrofit that is undone at the next refurbishment does not deliver neutrality across the lifetime of the new homes, so the mechanism has to include some assurance of longevity.
And the saving has to be evidenced. That means metered before and after data, or an accepted deemed saving per fitting type, with the assumptions stated.
Some authorities operate or contribute to a pooled offsetting scheme funded by developer contributions, which is faster for the applicant than assembling a bespoke retrofit. Where a scheme exists, the contribution is secured by planning obligation, and the level is set by the authority rather than negotiated per site.
What the application has to contain
The submission needs to let the authority complete a habitats regulations assessment, so it has to be specific enough for the conclusion to rest on it.
| Element | What to provide |
|---|---|
| Baseline | Existing water use on the site, if any, with the basis for the figure |
| Proposed demand | Litres per person per day, calculated using the Part G water calculator, with the fittings schedule |
| Occupancy | The occupancy assumption for each unit type and its source |
| Residual demand | Total additional abstraction in cubic metres a year |
| Offset | The measures, their location, the saving claimed, the evidence and the securing mechanism |
| Monitoring | How the saving will be verified after completion |
A Water Supply Assessment is the natural home for the supply side of this, covering the connection, network capacity and the undertaker's position. The efficiency and offsetting narrative usually sits in the Sustainability Statement, cross-referenced rather than repeated.
What it does not cover
Water neutrality is about abstraction. It does not deal with wastewater capacity, surface water flooding or drainage design, and an applicant who answers a water neutrality objection with a drainage strategy has answered the wrong question.
Foul capacity at the receiving treatment works is a separate matter for the undertaker and, on constrained networks, a real programme risk in its own right. That belongs in a Foul Sewage Assessment. Surface water design sits in a Drainage Strategy, where the relevant tests are run-off rates and the drainage hierarchy.
Illustrative example. A 30 unit scheme in an affected zone designs to a low per person demand using specified flow rates, which cuts the residual figure substantially without unusual technology. The remaining demand is met by a contribution to the authority's offsetting scheme, secured by a unilateral undertaking, and the habitats regulations assessment concludes on that basis. This example is illustrative only.
Programme, and one honest caveat
Treat the offsetting mechanism as the critical path. The efficiency calculation takes days. Securing an offset, agreeing the wording and completing the legal agreement takes months, and the authority cannot issue a decision until it is in place.
The caveat is worth stating plainly. Deemed savings from retrofit measures carry real uncertainty, and the evidence base for how much water a replacement fitting actually saves over years of use is thinner than the confidence with which the figures are quoted. Where the authority accepts deemed savings, use its published rates and say where they came from.
This is general guidance, not legal advice. Check the position with your local planning authority, the water undertaker and a qualified professional before relying on it.
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Frequently asked questions
What does water neutrality actually require?
That the development does not increase the rate of water abstraction from the environment above the pre-development level. Applicants work through three steps: reduce demand in the new development, offset the residual demand by reducing existing use in the same water resource zone, and only then consider new resources or other measures.
Where does water neutrality apply in England?
The best known case is the Sussex North water resource zone, covering parts of Horsham, Crawley and Chichester, following Natural England advice about abstraction affecting designated wetland sites in the Arun Valley. The boundary follows the water resource zone rather than the district, so check with the authority and the water undertaker.
What water use figure should a new home be designed to?
Building Regulations Part G sets 125 litres per person per day as the baseline and 110 litres as an optional requirement that a planning condition can impose. Affected areas expect a figure well below the optional requirement. Take the current target from the relevant strategy or council position statement rather than from an earlier scheme.
How is offsetting evidenced?
By showing that the saving is additional to work the water undertaker was already going to do, that it will last for the lifetime of the new homes, and that it can be measured. Metered before and after data or accepted deemed savings per fitting type, with the assumptions stated, are what authorities look for.
Is water neutrality the same as nutrient neutrality?
No. Both come from the habitats regulations and neither has a unit threshold, but water neutrality concerns abstraction while nutrient neutrality concerns nitrogen and phosphorus reaching a protected site. The calculations, the mitigation markets and the securing mechanisms differ, so satisfying one does nothing for the other.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.