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This guide is for water companies who operate water supply assets in England. This includes reservoirs, wells and boreholes.

Before you make certain discharges from your water supply assets to surface waters, you must get either:

• consent – under section 166 of the Water Industry Act 1991
• an environmental permit

When you need consent or a permit

You must consider each type of discharge you may make from your water supply asset to decide if you need consent or a permit.

Consent

You must have consent under section 166 of the Water Industry Act 1991 from the Environment Agency for discharges:

• that may contain solids or polluting matter
• of drawdown releases through the scour valve
• through pipes that are larger than 229mm diameter

You do not need consent for qualifying discharges from a pipe that is 229mm diameter or less. But you must take steps to make sure the discharge is as free from pollutants as is reasonably practicable.

Permits

Some discharges do not qualify for consent under the Water Industry Act 1991. You must have a permit from the Environment Agency for these discharges.

You do not normally need a permit for discharges that are:

• uncontaminated surface waters
• a water transfer and the discharge will not pollute
• made in an emergency to avoid danger to human health – but you must take all reasonably practicable steps to minimise pollution and tell the Environment Agency as soon as reasonably practicable

Before you apply for consent or a permit

You need to:

• assess the potential environmental and safety risks of your proposed discharge
• develop a management system – a written set of procedures that identify and minimise the risks of pollution

How to assess the risks

Your risk assessment will be part of the technical information that supports your consent or permit application.

The detail you need to provide depends on:

• the type of water supply asset
• the volume and duration of the discharge
• the sensitivity of the receiving water
• the potential for water quality impacts

For higher-risk discharges, you’ll need to complete a more structured supporting risk assessment. For example for discharges:

• from large storage reservoirs
• that are high‑volume, prolonged or into sensitive waters

For other water supply assets, you’ll need to provide information that’s proportionate to the environmental risk.

For lower-risk discharges, you can briefly explain why the risks are low and how you will manage them. For example, you could explain how you will manage solids settlement, dechlorination or other pollution controls.

When you apply, you’ll need to give enough information to show that your discharge will not cause unacceptable harm to the environment.

The Environment Agency will consider whether you have properly assessed the risks. You will only get consent or a permit if you have mitigated the risks as far as is reasonably practicable.

Increase in downstream flow

You must assess whether your water supply asset discharge will affect the downstream flow.

An increase in downstream flow can:

• damage property, bridges, boats and bankside structures
• affect land use, for example block access tracks
• risk the life and health of people and animals
• change the river’s appearance, for example erode the river bank
• damage the river ecology, for example wash away aquatic plants
• destroy fish habitats and breeding sites
• displace fish downstream

To reduce the impact you must control the:

• rate of your discharge
• volume of your discharge
• increase in the depth of the channel downstream

You must carry out routine drawdown operations to prevent or minimise downstream impacts and flood risks, as far as is practicable.

Your risk assessment must identify any properties or situations that your routine discharge operations may impact. For example:

• houses, businesses, caravan sites and campsites
• local water users like anglers, boaters and canoeists

You should maintain a contact register and give warning before drawdown operations.

Discharge of sediment

You must consider if the discharge from your water supply asset will impact sediments downstream. Significant deposits of sediments can:

• damage the river ecology
• destroy fish habitats and breeding sites
• change the river’s appearance

Consider surveying how much sediment has accumulated that could be washed through the scour valve. Include details of sediment levels in relation to the scour valve height and sediment sampling as part of your consent or permit application.

Your discharge is more of a risk if:

• you have not opened the scour valve for over one year
• there has been an event that could have created large amounts of sediment, for example a flood upstream of a reservoir

If a large quantity of sediment may wash through the scour valve, you must develop a plan to prevent a damaging discharge.

To reduce the impact, consider the following mitigation measures:

• coincide the discharge with higher natural river flows and increased natural sediment transport
• open the scour valve gradually
• make frequent small discharges
• install and maintain sediment traps to remove trapped sediment

Discharge of polluted sediment

You must consider if pollutants may be present in significant amounts in your water supply asset discharge sediment.

Discharge sediment containing pollutants may be carried into the downstream river and can:

• cause deterioration in river quality – for water users and abstractors
• damage the river ecology – in the short or long term

You must chemically test the sediment if it may contain pollutants.

To reduce the impact, consider dredging the polluted sediment from the water supply asset’s discharge. You must dispose of the dredged sediment safely.

Discharge of poor quality water

You must check whether your water supply asset discharge is subject to thermal stratification. Thermal stratification is where there are changes in temperature and dissolved oxygen at different depths.

Discharges of stratified water can lower the levels of dissolved oxygen and increase levels of iron and manganese. This can:

• cause deterioration in river quality – for water users and abstractors
• kill fish and other aquatic animals

For stratified reservoirs, your risk assessment must include profiling for:

• dissolved oxygen
• temperature

The Environment Agency is unlikely to allow a discharge if profiling shows the dissolved oxygen is below 50% saturation in the bottom profile of the reservoir.

If your profiling shows less than 80% dissolved oxygen, you should monitor the downstream watercourse during the discharge. Your risk assessment should set a downstream trigger limit for dissolved oxygen. If dissolved oxygen levels drop below this limit, stop the discharge and notify the Environment Agency.

Algal blooms in reservoirs can cause poor quality discharge water. You should not make planned discharges if there is a significant algal bloom, unless you have shown that the bloom does not affect the discharge quality.

Impact on fish

Discharges of water can displace fish from a reservoir into the downstream river.

You must consider the impact on fish if you plan a substantial drawdown. This includes drawdown to a permanently lower water level and also to temporary lower water levels for maintenance before you refill.

You should contact the Environment Agency and ask to speak to your local fisheries team. You may need to rescue the fish so you can relocate them elsewhere or restock them after you’ve refilled the reservoir.

Apply for consent

Apply for consent under section 166 of the Water Industry Act 1991 using the online form. You will need to provide:

• details about the discharge and its location
• your site plan
• information on the risks and how you will mitigate them

Apply for a permit

If you cannot get consent to discharge under section 166 of the Water Industry Act 1991, check how to apply for a permit instead.