Water is one of those utility costs that tends to sit quietly in the background. The bills arrive, they seem roughly consistent with previous quarters, and they get approved without detailed scrutiny. Compared to energy, the amounts are smaller. The bills are shorter. The urgency feels lower.

This is understandable - and it's exactly the reason water billing errors persist undetected for years in many commercial organisations.

A commercial water audit is an independent, line-by-line review of your business water and wastewater bills, infrastructure records, and rateable value assessments. It identifies errors, overcharges, and historical overpayments - and recovers them on your behalf.

This guide explains what a water audit actually involves, what it typically finds, who benefits most, and how the recovery process works.

Section 1 - Why water bills are harder to verify than you think

Commercial water billing in the UK is more complex than it appears on the surface. Unlike energy, where you broadly pay a unit rate for what you consume, commercial water charges are made up of several distinct components - some consumption-based, some fixed, and some calculated using assessments that may not have been reviewed in years.

The main components of a commercial water bill:

• Volumetric charges - based on actual metered consumption of water supplied
• Surface water drainage - based on the rateable value of your property and the area of impermeable surface that drains into the sewer network
• Trade effluent charges - if your business discharges anything other than domestic wastewater to the sewer, you may be paying trade effluent rates
• Rateable value charges - some elements of the bill are calculated using the rateable value of your property, which may be outdated or incorrect
• Highway drainage - a fixed charge for public drainage infrastructure serving your site
• Standing charges - fixed daily or annual charges regardless of consumption

The rateable value element is particularly important. Rateable values for many commercial properties were last assessed years ago, and if your property has changed use, been subdivided, reduced in size, or had infrastructure modifications, the assessed value used to calculate your water charges may no longer be accurate.

Section 2 - What a commercial water audit reviews

A thorough water audit covers several distinct areas:

Metered consumption accuracy

Are the meter readings on your bills accurate? Are estimated reads being used where actual reads should be taken? For sites with multiple meters - separate supplies for irrigation, cooling, production processes, or welfare facilities - are all meters accounted for correctly?

Metering errors are common, particularly on complex sites where infrastructure has changed over time. A meter that was installed for a specific purpose and then disconnected or bypassed may still be generating standing charges.

Surface water drainage charges

Surface water drainage charges are calculated based on the area of impermeable surface on your site that drains to the public sewer network. If your site has permeable surfaces, sustainable drainage systems (SuDS), or areas that drain to a watercourse rather than the public sewer, you may be paying drainage charges on surfaces that should be exempt.

The calculation requires a physical assessment of the site - which is why an eyebright specialist attends your site as part of the water audit process. The assessment can typically be completed within a few hours, depending on the size and complexity of the site.

Rateable value accuracy

As noted above, rateable value is used as the basis for several water charge components. If your property's rateable value is incorrect - which is not uncommon, particularly where properties have been modified, subdivided, or changed use - the charges based on it will also be incorrect.

Recovering overcharges where rateable value errors exist can cover up to six years in England and five years in Scotland.

Trade effluent and wastewater

If your business produces wastewater that contains anything other than domestic sewage - trade effluent from manufacturing processes, commercial kitchens, laundries, vehicle washing, or similar activities - you need a trade effluent consent from your water company. The charges applied to trade effluent vary significantly based on the volume and strength of the discharge.

Both overcharging and undercharging occur in this area. An audit will confirm whether your consented volumes, strength assessments, and resulting charges are accurate.

Section 3 - What water audits typically find

The frequency and scale of findings varies by organisation, but some categories of error are particularly common:

• Surface water drainage overcharges are consistently the most common finding, particularly on sites where hard standing has been replaced with permeable surfacing, or where drainage infrastructure has been modified. Many organisations are paying drainage charges on surfaces that have been exempt for years.
• Rateable value discrepancies are common where properties have had planning changes, structural modifications, or changes of use that weren't reflected in the rating assessment used for water charging purposes.
• Meter errors and estimated reads - particularly on sites with multiple meters, where some supplies may have been capped or decommissioned but charges continue.
• Incorrect standing charges - particularly after supplier changes or where contract terms haven't been correctly applied to all meters on a site.
• Trade effluent misclassification - either charges applied where no trade effluent consent should be needed, or consent volumes that don't reflect actual discharge patterns.

Section 4 - Who benefits most from a water audit

Water audits deliver the strongest results for:

• Large or complex sites with multiple meters, significant hard standing, or a mix of supply types. The more infrastructure on site, the higher the probability that something isn't being charged correctly.
• Manufacturing, food and drink, and hospitality - sectors with significant process water use, large impermeable surfaces, and trade effluent discharge requirements. These organisations typically have the highest water spend and the most complex billing structures.
• Multi-site portfolios - property managers, retail groups, and multi-site operators where individual site bills rarely receive scrutiny. Portfolio-wide audits frequently find systemic errors replicated across multiple sites.
• Sites that have undergone changes - any significant development, change of use, surface modification, or infrastructure upgrade creates the potential for billing records to fall out of step with the actual site.
• Long-standing supplier relationships - where bills have been approved on autopilot for years and have never been independently reviewed.

Section 5 - How the recovery process works

The water audit process follows a similar structure to an energy revenue recovery audit:

• Letter of Authority - you authorise eyebright to contact your water company and request data on your behalf
• Site assessment - an eyebright specialist attends your site to assess drainage areas, meter locations, and infrastructure in detail
• Data analysis - billing data, meter records, rateable value assessments, and trade effluent consents are reviewed line by line
• Findings report - every identified error and overpayment is documented and quantified
• Recovery negotiation - eyebright takes findings to your water company and manages the refund process on your behalf
• Refund delivered - recovered funds returned as a credit against future bills or direct payment

The audit operates on a share-of-savings basis. There is no upfront cost. If nothing recoverable is found, there is no charge - and the audit still provides reassurance that your billing is correct and that no overpayments have been missed.

Section 6 - Water audit vs energy audit: doing both makes sense

Many organisations commission a water audit at the same time as an energy revenue recovery audit. There's a logical efficiency argument: the same Letter of Authority process, the same data-gathering infrastructure, and the same forensic approach applied across both utilities simultaneously.

For multi-site organisations with significant utility spend, running both audits in parallel is usually the highest-return activity available before any procurement strategy work begins. You want to know you're starting from an accurate billing baseline before you negotiate new contracts.

The bottom line

If your business water bills have never been independently reviewed, there's a reasonable probability that you're paying for something incorrectly. Surface drainage, rateable value, and meter accuracy are all areas where errors compound quietly over years.

The only way to know is to look - and the economics of a share-of-savings audit make looking entirely risk-free.

Find out if your water bills are correct.

Request a free water audit review. We'll confirm whether an audit is likely to find value at your scale - at no cost and no obligation.

Request a Free Audit