Guide to completing the nutrient calculator

Nutrients are chemicals which plants need to grow. However, when waterways have high levels of nutrients like nitrates and phosphorous, this can cause the growth of too much algae, which kills off fish and shellfish and damages habitats.

New developments can result in additional nutrients entering the waterways. This is usually through the wastewater that new developments generate.

Following a European Court Case, Natural England, who are the Government’s advisor on natural environment matters, confirmed that new developments should not result in an increase in nutrient pollution to the waterways.  As such, new developments within the Solent area must demonstrate “nitrate neutrality” before they can progress.

Nitrate neutrality means that developments should not generate additional nitrates, or that any nitrates that result from new development are offset by removing nitrate pollution elsewhere in the river catchment.  Using water efficiency measures and sustainable drainage systems (SUDs) helps to reduce the amount of nitrate pollution a development will cause, but it is difficult to ensure that new dwellings do not result in any additional nitrate discharge into the local watercourse. As such, removing nitrates elsewhere within the river catchment is a way that nitrate neutrality can be met. This is usually achieved by purchasing credits from certified schemes that removes another polluting use (most commonly by taking active agricultural land out of production). 

• New dwellings – either by conversion or new build
• New student accommodation
• New care homes
• New hotel or any other overnight accommodation
• New Sui Generis Houses in Multiple Occupation (with 6+ occupants) or those providing an additional bedroom
• Commercial or industrial processes that generates additional nitrate pollution

The first step is to complete the nutrient calculator (Natural England nutrient calculator and guidance - Partnership for South Hampshire). The calculator provides a figure which is the level of additional nitrates that your development will generate. This information is needed for your planning application to be registered.  Your planning application will remain INVALID without it.

You will also need to complete the Council’s Sustainability checklist.

The results of the calculator will be used to inform the amount of nitrates credits that you will need to purchase before the development can proceed – assuming planning permission is granted.

The nutrient calculator is a spreadsheet which you need to fill in before submitting your planning application. The calculator needs to be submitted with your application for your application to be processed.

For Southampton the Solent: nutrient neutrality calculator - GOV.UK should be used.

The Government has provided a detailed guide which breaks down how to complete the spreadsheet: Using the nutrient neutrality calculators - GOV.UK.

There is some information that you will need to find out before starting the calculator. The starting point is to find out which river catchment your site lies within.

The calculator spreadsheet has five tabs and you will need to fill in the first four. The last tab is calculated automatically based on the information you have provided.

The following is a summary of some of the frequent queries customers have when completing the spreadsheet.

• Visit the catchment planning page on GOV.UK
• Enter postcode of application site
• On the search results screen, Filter by 'Operational Catchments'
• Zoom in to your site on the map and left click on the location of the site. The text in the speech bubble over the map will be the relevant catchment

This is the date when people will start living or using the project that you are planning. If the development is speculative or you’re unsure you should provide a well-informed guess.

Southampton have provided a simple spreadsheet to work this out.

For HMOs and purpose-built student studio flats the occupancy will be one person.

The calculator spreadsheet has pre-inserted amount of 120 litres per day. In Southampton, to meet our policies we require developers to achieve water savings that result in use of no more than 100 litres per day. As such, this can be adjusted to 100 for the spreadsheet and a planning condition will be used to ensure any subsequent planning permission restricts the water use of the development.

This is the number of dwellings that will be in your development once it has been finished.  In the case of HMOs, treat each bedspace as one dwelling.

You need to carry out two calculations: fill in the calculator for the size of the existing HMO (for example, an existing 6-bed HMO would be 6 dwellings with an occupancy of 1). Next fill in the calculator for the proposed HMO (for example, a proposed 7-bed HMO would be 7 dwellings with an occupancy of 1). You then subtract the Total Annual Nitrogen budget for the existing HMO from the Total Annual Nitrogen Budget for the proposed HMO. The end figure is the nitrogen budget for your development.

Select 'yes' for sites in Southampton.

Select from the dropdown menu based on which area your site lies within as follows:

Millbrook Wastewater Treatment Works serves Bargate, Banister & Polygon, Bevois, Freemantle, Millbrook, Shirley, Coxford & Redbridge.

Portswood Wastewater Treatment Works serves Bitterne Park, Swaythling, Portswood & Bassett.

Woolston Wastewater Treatment Works serves Woolston, Peartree, Sholing, Harefield and Thornhill.

• Visit the Soilscapes Viewer
• Search by the site postcode
• You have to select one of the following soil types:
  • Freely draining
  • Slightly impeded drainage
  • Impeded drainage
  • Variable
  • Surface wetness
• To the right of the map the soil type is provided. In the example below, the input for the calculator spreadsheet would be “freely draining”

• Visit Catchment Info for Station 4209 - Tanners Brook at Millbrook
• Zoom into the map to find your site
• Select 'rainfall' from the 'Select data type to view' menu
• Use the result to select from the correct range from the drop-down menu within the calculator spreadsheet. In Southampton, the range is between 675-750

The whole of Southampton is within a nitrate vulnerable zone so your answer will be ‘Yes’.

• Select the existing land use from the drop-down menu
• In Southampton, this will typically be residential urban land or commercial urban land
• Then input the site area in hectares. To convert sq.m to hectares, divide the square meterage by 10,000
• Garden land would fall within the residential urban land category, as would include any associated roads, driveways or grass verges
• Open urban land would be open spaces such as playing fields or sports pitches

• Select the proposed land use(s) from the drop-down menu
• Input the areas of the uses in hectares. To convert sq.m to hectares, divide the square meterage by 10,000

If you are not proposing any sustainable urban drainage systems for your development, then the SUDS catchment area figure and the percentage of the flow entering the SUDs will be “0”.  If you have designed a SUDS scheme for your application, your drainage engineer can help fill in this part of the calculator.

The last tab of the spreadsheet provides you with a “Total Annual Nitrogen Load to Mitigate”. Once planning permission is granted, a condition will usually be imposed on your permission which requires you to purchase the necessary credits to mitigate that nitrogen load. As such, it is important to correctly complete the calculator so you only purchase what you need to.

There are a number of mitigation projects for your scheme to use, but the simplest is operated by Eastleigh Borough Council with details available using this link: Nutrient Neutrality.