Borehole Drilling and Private Water Supplies Across Oxfordshire

Borehole Service Utilities Ltd drills water boreholes across Oxfordshire, from the Chalk of the Chilterns and the Berkshire Downs to the Cotswold limestone in the west and the Corallian ridge that separates the Thames valley from the Vale of White Horse. The company installs private water supplies for houses, farms, estates, nurseries, sports grounds and businesses, and looks after them afterwards. That means the whole job under one contract: siting and survey, drilling, casing and screening, test pumping, the pump and controls, filtration, and the sampling that shows the water is fit to use.

Oxfordshire is good borehole country. The British Geological Survey and the Environment Agency describe the Corallian aquifer as still supplying many farms, nurseries, market gardens, golf courses and domestic users, and the Chalk beneath the Chilterns and the Berkshire Downs is the most productive formation in the county. What varies is depth, yield and water chemistry, and all three change over short distances. A borehole at Nettlebed on the Chiltern dip slope is a different job from one at Marcham on the Corallian, or one in the ironstone at Hornton. Call 01428 735013 to talk through a specific site.

Private water supply boreholes for Oxfordshire homes, farms and estates

A water well borehole gives a property its own supply, drilled into the rock beneath the site and pumped up to a storage tank or into the house main. Borehole Service Utilities Ltd drills private water supply boreholes across Oxfordshire for households, farms, estates, commercial growers and businesses. Most single households use far less than the 20 cubic metres a day at which Environment Agency abstraction licensing starts, so for a domestic supply the questions are usually geology, access for the rig and where the borehole can safely sit, rather than a licence application.

The reasons for drilling vary. Some properties have never had mains water, which is common in the ironstone villages north of Banbury, on the Chiltern dip slope around Nettlebed and Stoke Row, and in the vale hamlets under the downs. Others have a mains connection but not enough water from it: a farm filling troughs, a nursery watering stock beds, or a house at the end of a long shared private main where summer pressure falls away. Thames Water supplies mains water across Oxfordshire, and a borehole is often run alongside the mains rather than instead of it.

A borehole is a permanent asset attached to the land. Once it is drilled, cased, tested and commissioned, the running costs are electricity for the pump, filter and lamp changes, servicing and water testing. Yield is the thing to settle honestly at the start. In limestone and Chalk the water arrives through fissures, so what a borehole gives depends on the fractures it intersects rather than on how deep it goes. That is why test pumping matters far more than a drilling depth written on a quote.

The geology under Oxfordshire, and what it means for your borehole

Four water-bearing formations matter for boreholes in Oxfordshire, and which one lies under the site decides the depth, the likely yield and the treatment. The Chalk Group of the Chilterns and the Berkshire Downs is a principal aquifer and the most productive formation in the county. The Great Oolite and Inferior Oolite limestones carry the Cotswold west and north-west. The Corallian Group, Jurassic limestone and calcareous sandstone, forms the low ridge between the Thames, or Isis, valley and the Vale of White Horse. In the north, the thin Marlstone Rock ironstone around Banbury is a minor aquifer only.

BGS classes the Corallian as an important minor aquifer rather than a principal one. It is usually about 35 metres thick in this area, with only around 20 metres of usable aquifer near Oxford, although a 78 metre sequence was recorded at Harwell. Domestic and farm supplies on or close to the outcrop are normally completed within the first few tens of metres to about 80 metres. Yields are typically 25 to 85 cubic metres a day, and much higher figures have been recorded at favourable sites: 1,425 cubic metres a day at Cowley, up to 800 near Abingdon and 660 at Wootton.

Chalk depth is governed by where the water table sits, not by a standard figure. BGS records that the most productive fractures are in the upper part of the aquifer, in the zone of water table fluctuation, probably the top 50 metres or so, with permeability very low below that. A working band of 30 to 100 metres is a reasonable indicative range for Chalk in south-east England, but a hilltop property above Henley needs a materially deeper hole than one at the scarp foot near Watlington. Down dip of the Corallian outcrop, south and south-east of Abingdon, the aquifer is confined, artesian conditions occur, and the water turns highly mineralised and non-potable within 5 to 6 kilometres.

The formations under Oxfordshire, and what each one usually means:

  • Chalk Group, Chilterns: Henley-on-Thames, Nettlebed, Stonor, Watlington, Chinnor, Stoke Row and Checkendon. A principal aquifer giving hard water that is naturally low in iron, reaching the borehole through fissures.
  • Chalk Group with Upper Greensand beneath, Berkshire Downs: the Letcombes, Sparsholt, Childrey, the Hendreds, Blewbury and Harwell, and west along the scarp through Uffington and Ashbury. Deeper holes are needed on the high downland than below the scarp.
  • Great Oolite and Inferior Oolite: Chipping Norton, Charlbury, Burford, the Wychwoods, Woodstock, Witney, Bampton and Carterton. A principal aquifer with highly variable yield. At one Cotswold site BGS found the productive fractures in the Great Oolite at roughly 35 to 76 metres and in the Inferior Oolite at about 100 to 132 metres.
  • Corallian Group: the low ridge running through Abingdon, Wantage, Didcot and Shrivenham. Hard calcium-bicarbonate water, with dissolved iron the usual treatable issue.
  • Marlstone Rock, Middle Lias: Banbury, Hornton, Wroxton, Shenington, Bloxham, Deddington and Hook Norton. Typically about 3 metres thick, up to 7.5 metres in the Banbury area, and borehole yields are rarely over 40 cubic metres a day.
  • Lower Greensand around Faringdon: highly lenticular, so thickness and water-bearing capacity change over short distances and cannot be assumed from a neighbouring borehole.
  • Oxford Clay, Kimmeridge Clay and Gault: no supply is taken from the clays themselves. They confine the aquifers beneath them and they are the reason conventional soakaways fail across much of the county.

Where in Oxfordshire Borehole Service Utilities Ltd works

Around Oxford the work is on the farmland and the college and private estates immediately outside the ring road, in the fringe parishes of OX2, OX3 and OX4: Cumnor and Wytham, Elsfield, Beckley and Stowood, and Sandford-on-Thames. South of the city, the Corallian belt around Abingdon-on-Thames (OX13 and OX14) takes in Frilford, Marcham, Appleton-with-Eaton, Longworth and Kingston Bagpuize with Southmoor, which is prime private-supply country. Didcot (OX11) reaches south onto the Chalk of the Berkshire Downs at Blewbury, Chilton, Upton, Harwell, East and West Hagbourne, Aston Tirrold and Aston Upthorpe.

In the Vale of White Horse the ground climbs from Wantage (OX12) onto the downland at Letcombe Regis and Letcombe Bassett, Sparsholt, Childrey, Kingston Lisle, East and West Hendred, Ardington and Lockinge. Faringdon sits in SN7, a Wiltshire-looking postcode that is entirely Oxfordshire, with Buscot, Buckland, Pusey, Uffington, Stanford in the Vale and Great Coxwell. Shrivenham, Watchfield, Ashbury, Compton Beauchamp and Bourton and Coleshill fall in SN6. North Oxfordshire runs from Banbury (OX15, OX16 and OX17) out to the ironstone villages at Bloxham, Adderbury, Deddington, Wroxton, Hornton, Shutford, the Sibfords, Cropredy, Wardington and Shenington.

Bicester (OX25, OX26 and OX27) covers the arable and estate country at Steeple Aston, Middleton Stoney, Somerton, North Aston, Merton, Fringford, Stratton Audley, Hethe and Stoke Lyne. West Oxfordshire takes in Witney (OX28 and OX29) with Eynsham, Standlake, Stanton Harcourt, Minster Lovell, Freeland, Church and Long Hanborough, Northmoor and Stonesfield; Burford and Carterton (OX18) with Bampton, Clanfield, Alvescot, Shilton, Taynton, Swinbrook and Widford, Asthall, Black Bourton and Brize Norton; Chipping Norton and Charlbury (OX7) with Hook Norton, Great and Little Tew, Heythrop, Enstone, Kingham, Chadlington, Churchill, the Wychwoods, Spelsbury, Finstock, Fawler and Ramsden; and Woodstock (OX20) with Bladon, Glympton, Kiddington with Asterleigh and Wootton.

In the south-east of the county, on and under the Chalk of the Chilterns:

  • Henley-on-Thames (RG9) and the beechwood and estate country at Nettlebed, Bix and Assendon, Pishill with Stonor, Highmoor, Rotherfield Greys, Rotherfield Peppard, Stoke Row, Nuffield and Swyncombe, where a high proportion of large houses are on private supplies.
  • Goring-on-Thames (RG8) in the Goring Gap, where the Thames cuts the Chalk between the Chilterns and the Berkshire Downs, with Woodcote, Goring Heath, Checkendon and South Stoke.
  • Watlington (OX49), entirely rural and entirely South Oxfordshire, with Shirburn, Pyrton, Britwell Salome, Brightwell Baldwin, Cuxham with Easington and Lewknor.
  • Chinnor (OX39) under the escarpment, with Crowell, Sydenham and Kingston Blount.
  • Thame (OX9) and the mixed arable and grazing at Tetsworth, Adwell, Wheatfield and Stoke Talmage.
  • Wallingford (OX10), wholly South Oxfordshire, with Ipsden, Ewelme, Cholsey and Moulsford.
  • A note on postcodes: OX7, OX9, OX12, OX15, OX17, OX18, OX27, OX39, RG8, RG9 and SN6 all extend beyond the county boundary, so check a full postcode rather than assume a whole district is in Oxfordshire.

What happens on site, from survey to commissioning

Every borehole starts with an assessment before a rig is booked. Borehole Service Utilities Ltd looks at the formation under the site, the records of nearby boreholes, the likely water table, and where the borehole can sit: clear of drains, tanks, slurry, fuel stores and the reach of a septic system, with room for a rig and its support vehicle. Anyone sinking a borehole to search for or abstract water more than fifty feet, about 15 metres, below the surface must notify UK Research and Innovation before work begins, and that notification is handled as part of the job.

Drilling a domestic borehole is usually a matter of days rather than weeks, although depth, ground conditions and access all move the programme. The upper section is cased and the annulus grouted to seal the borehole against surface water. That matters in Oxfordshire, because BGS records that soils over much of the Corallian outcrop have high or intermediate leaching potential and give little protection against pollution from the surface. Below the casing the borehole is completed open-hole or screened, then developed to clear the drilling fines and open up the fissures feeding it.

Test pumping turns a hole in the ground into a known supply. The borehole is pumped at measured rates while water levels are recorded, which gives the sustainable yield and the depth the pump should be set at. A sample goes to a laboratory. Only then is the down-hole pump sized and installed, with the rising main, control panel, pressure vessel or storage tank and any treatment. A journal of the strata passed through, the levels at which water was struck and the flow test results goes to UKRI on completion.

The usual sequence on an Oxfordshire water borehole:

  • Assessment of the geology and nearby borehole records, then a site visit to settle where the borehole goes and how the rig gets to it.
  • Notification to UK Research and Innovation for any water borehole deeper than about 15 metres.
  • Drilling, with the upper section cased and grouted to seal out surface water.
  • Completion open-hole or with screen and gravel pack, then development to clear drilling fines.
  • Test pumping at measured rates to establish the sustainable yield and the pump setting depth.
  • Laboratory analysis of a water sample, which decides the treatment train.
  • Pump, rising main, controls, storage and filtration installed and commissioned, and the borehole record filed.

Do you need a licence for a borehole in Oxfordshire?

An abstraction licence is required from the Environment Agency for most types of water abstraction over 20 cubic metres a day. Below that figure most abstraction falls outside the licensing requirement, but exemptions and special cases exist, so the right course is to check rather than to assume. A single household in Oxfordshire is comfortably under the threshold. A farm, estate, nursery, sports ground or golf course irrigation supply can pass it easily, and that is a conversation to have before drilling rather than after. A temporary licence covers taking more than 20 cubic metres a day for a period of less than 28 days.

Section 198 of the Water Resources Act 1991 requires anyone intending to sink a well or borehole to search for or abstract water to more than fifty feet, about 15 metres, below the surface to notify UK Research and Innovation before sinking begins. A journal must be kept of the strata passed through and the levels at which water was struck, together with particulars of any flow tests, meaning rates, duration and water levels during and after testing, and a copy sent to UKRI on completion or abandonment. Failure to comply is an offence carrying a fine not exceeding level 3 on the standard scale.

Once a private supply is in use, the Private Water Supplies (England) Regulations 2016 bring in the local council, which in Oxfordshire means Cherwell, West Oxfordshire, South Oxfordshire, Vale of White Horse or Oxford City depending on where the property sits. The authority must risk-assess private supplies in its area and review that assessment at least every five years. For a single dwelling the test is whether the supply is provided as part of a commercial or public activity: where it is, the duty applies; where it is not, the council assesses the supply if the owner or occupier asks. Sampling then follows from the risk assessment.

Filtration, treatment and keeping an Oxfordshire borehole working

Oxfordshire groundwater is hard, and on the Corallian dissolved iron is the usual treatable problem. In the BGS and Environment Agency baseline study of the Corallian, more than half the samples exceeded the 200 microgram per litre drinking water limit for iron, with a median of 354 micrograms per litre where the aquifer is confined against 84 micrograms per litre where it is unconfined. Manganese is comparatively low, so the two should not be assumed to arrive together here. Measured pH averaged 7.35 and groundwater temperature ranged from 9 to 17.2 degrees Celsius.

On the Chalk and the Cotswold limestones the risk is different. BGS records that the Chalk has insignificant matrix permeability and works as an aquifer through its fracture network, and that work on turbidity and bacteriological occurrence in Chalk boreholes has revealed rapid groundwater flow. Genuine karst development is documented in the Great and Inferior Oolite. In practice that means water can turn cloudy after heavy rain and surface organisms can travel quickly, so sediment pre-filtration with ultraviolet disinfection is the normal answer, with scale management for the hardness. In the Marlstone around Banbury, BGS reports water that is generally good but hard and often ferruginous, with nitrate above the 50 milligram per litre limit recorded at some sources.

Treatment is only useful if it is maintained, and a borehole is a piece of plant. Borehole Service Utilities Ltd services pumps and controls, changes filter cartridges and ultraviolet lamps, investigates falling yield, chases water quality changes, runs down-hole CCTV surveys and carries out borehole rehabilitation where a screen or the surrounding formation has silted or encrusted. A borehole that has gone off is rarely beyond help. Most faults trace back to the pump, the pressure system, a failed seal, or a treatment stage that has been left too long between services.

Treatment stages commonly fitted on Oxfordshire private supplies:

  • Sediment and particle filtration, the first stage on any supply fed by fissure flow.
  • Iron removal, most often needed on the Corallian and in the north Oxfordshire ironstone.
  • Ultraviolet disinfection against bacteria, standard where water reaches the borehole through fractures.
  • pH balancing where analysis puts the water at the acidic end of the range.
  • Limescale reduction for the hard calcium-bicarbonate water the county's limestone and Chalk produce.

Irrigation boreholes and off grid supply for land and remote property

An irrigation borehole gives a garden, sports ground, golf course, nursery or farm its own water for the months when it is needed most. Borehole Service Utilities Ltd drills and equips irrigation supplies across Oxfordshire. BGS and the Environment Agency name farms, nurseries, market gardens and golf courses as established users of the Corallian aquifer, which is exactly the pattern through the Vale of White Horse and the belt running from Abingdon to Wantage, Didcot and Shrivenham. Irrigation demand often passes the 20 cubic metre a day threshold, so licensing is settled at the design stage rather than after the rig has left.

The county's land use explains the demand. Most of the ground over the Corallian is arable, growing wheat, barley, oilseed rape, linseed, vegetables and orchard fruit, with potatoes doing well on the sandier soils, alongside grassland, mixed livestock and dairying. Littlebrook Nurseries at Northmoor near Witney has grown semi-mature container trees, box topiary and pleached hornbeams on site since 1993, and Brightwell Vineyard a mile north of Wallingford covers 16 acres of eight varieties. Estate and equestrian land runs right through the county, from Blenheim at Woodstock, host of the Blenheim Palace International Horse Trials, to the stud and livery yards of the north Oxfordshire ironstone villages.

Off grid solutions cover the properties with no mains water and no convenient power either. A solar-powered down-hole pump runs the borehole from a photovoltaic array instead of a grid connection, filling a storage tank through the day so the property draws from stored water rather than from instantaneous pumping. That suits remote farmsteads, fields and buildings well away from a supply, which is the pattern on the downland above Wantage, in the Chiltern beechwoods around Pishill and Nettlebed, and on the Cotswold plateau. Sizing is worked out on daily volume and the height the water has to be lifted, not on peak flow alone.

Soakaway boreholes where Oxfordshire ground will not take surface water

A soakaway borehole disposes of surface water by drilling through low-permeability ground into a permeable formation below, so the water reaches rock that will accept it. It is the standard answer where a percolation test fails and a conventional soakaway pit cannot work. Across large parts of Oxfordshire the culprit is clay: the Oxford Clay around the city, Otmoor and the Bicester lowland, the Kimmeridge Clay on the floor of the Vale of White Horse, and the Gault beneath the Chalk scarp. Otmoor, north-east of Oxford, is a low-lying wet clay basin, exactly the ground where surface water will not percolate.

Depth is set by the site rather than by a standard figure, because it depends on how far down the receiving limestone or Chalk sits at that particular spot. Where the Corallian or the Oolite is confined beneath clay, the borehole has to pass through the full thickness of that clay before it reaches anything permeable. On the Chalk dip slope the receiving formation may be far closer to the surface. A trial borehole and a falling-head test tell you what the ground will actually accept before a drainage design is finalised.

Permissions matter here. The Environment Agency and the lead local flood authority should be consulted before surface water is discharged to ground, and the Agency's concern typically arises where foul water is involved or where the discharge sits close to an aquifer used for water supply. In Oxfordshire that is a live consideration, because much of the county sits over the Chalk, the Oolites or the Corallian, and BGS records high soil leaching potential over much of the Corallian outcrop. Sealing the upper section and keeping the headworks tight is part of the design, not an extra.

Borehole drilling by town and postcode in Oxfordshire

These are the 20 main towns and postcode districts Borehole Service Utilities Ltd covers in Oxfordshire. The surrounding villages and outlying farms in each of these districts are covered too, so it is worth ringing even if your own village is not named here.

  • Oxford – OX1, OX2, OX3, OX4
  • Banbury – OX15, OX16, OX17
  • Bicester – OX25, OX26, OX27
  • Witney – OX28, OX29
  • Abingdon-on-Thames – OX13, OX14
  • Didcot – OX11
  • Thame – OX9
  • Wallingford – OX10
  • Wantage – OX12
  • Faringdon – SN7
  • Chipping Norton – OX7
  • Burford – OX18
  • Woodstock – OX20
  • Carterton – OX18
  • Henley-on-Thames – RG9
  • Watlington – OX49, RG9
  • Chinnor – OX39
  • Charlbury – OX7
  • Goring-on-Thames – RG8
  • Shrivenham – SN6

Borehole Questions from Oxfordshire Property Owners

It depends on the formation under the site. On the Corallian around Abingdon, Wantage and Didcot, domestic and farm supplies are normally completed within the first few tens of metres to about 80 metres, because the Group is only around 35 metres thick in this area. In the Chalk of the Chilterns and the Berkshire Downs an indicative band of 30 to 100 metres is reasonable, governed by how far the property sits above the water table. Only a site assessment settles the figure.

An abstraction licence is required from the Environment Agency for most types of water abstraction over 20 cubic metres a day. A single household is comfortably below that threshold, but farm, estate, nursery, sports ground and golf course irrigation can exceed it, and exemptions exist, so check before drilling. Separately, section 198 of the Water Resources Act 1991 requires notification to UK Research and Innovation before sinking any water borehole more than fifty feet, about 15 metres, deep.

Yield varies by formation and by the fissures a borehole intersects. In the Corallian, typical yields are 25 to 85 cubic metres a day, although much higher figures have been recorded at favourable sites: 1,425 cubic metres a day at Cowley, up to 800 near Abingdon and 660 at Wootton. In the Marlstone Rock around Banbury, borehole yields are rarely over 40 cubic metres a day. The Chalk is the county's most productive aquifer. Test pumping gives the real figure for a site.

Usually, once it has been tested and treated to suit the analysis. Oxfordshire groundwater is hard calcium-bicarbonate water. On the Corallian, more than half the samples in the BGS and Environment Agency baseline study exceeded the 200 microgram per litre limit for iron, so iron removal is common. In the Chalk and the Cotswold limestones water reaches the borehole through fractures, which can carry surface organisms and post-rainfall turbidity, so sediment filtration with ultraviolet disinfection is the normal treatment.

Drilling a domestic borehole is normally a matter of days on site rather than weeks, but the full programme is longer than the drilling. Time is needed for the assessment and siting, notification to UK Research and Innovation, development and test pumping, laboratory analysis, and then installing and commissioning the pump, controls and treatment. Depth, ground conditions and access for the rig all move the dates, which is why a programme is given per site.

Yes. Thames Water supplies mains water across Oxfordshire, and many properties run a borehole alongside a mains connection rather than instead of it. That is common where the mains is adequate for the house but not for irrigation, livestock or a nursery, or where summer pressure drops at the end of a long shared private main. The two systems are kept properly separated, and there is no requirement to give up the mains in order to have a borehole.

They fail because much of the county sits on clay that will not take water: the Oxford Clay around Oxford, Otmoor and the Bicester lowland, the Kimmeridge Clay in the Vale of White Horse, and the Gault under the Chalk scarp. A soakaway borehole is drilled through the clay into permeable limestone or Chalk below, so surface water reaches ground that will accept it. The Environment Agency and the lead local flood authority should be consulted before discharging surface water to ground.

A borehole needs servicing like any other item of plant. That means pump and control checks, filter cartridge changes, ultraviolet lamp replacement on schedule, and regular water sampling. Under the Private Water Supplies (England) Regulations 2016 the local council must risk-assess private supplies in its area and review that assessment at least every five years. Where yield falls or water quality changes, a down-hole CCTV survey and borehole rehabilitation usually find and fix the cause.

The whole county. That includes Oxford and its fringe parishes, Abingdon-on-Thames, Didcot, Wantage, Faringdon and Shrivenham in the Vale of White Horse, Banbury and Bicester in the north, and Chipping Norton, Charlbury, Burford, Carterton, Witney and Woodstock in the west, along with Thame, Wallingford, Watlington, Chinnor, Goring-on-Thames and Henley-on-Thames in the south-east. Several postcode districts cross the county boundary, so check a full postcode. Call 01428 735013.

Talk to a borehole contractor about your Oxfordshire site

Borehole Service Utilities Ltd works across Oxfordshire, from the Chiltern beechwoods to the Cotswold plateau and the Vale of White Horse. Tell us where the site is, what the water is for, and whether there is mains water or power on the land, and you will get a straight answer on what is likely to be under the ground there and what it would take to reach it. Call 01428 735013, or use 07970 573840 or 07517 151270, or email info@boreholeservice.co.uk.