Rainwater Harvesting Control System – UK-DIY

You need to know before go. At very end you will be redirected how to build it DIY

What is a Rainwater Harvesting Control System?

A rainwater harvesting control system is used to manage water stored in tanks, ensuring that water is available when needed while protecting pumps, plumbing, and the mains water supply.

The system monitors the water level inside a storage tank and controls connected equipment such as pumps and valves.
Its purpose is to maintain reliable operation, prevent dry running, and automate water top-up where required.

In simple terms, it acts as the decision-making unit of a rainwater or storage tank system.

Why is a control system needed?

Without proper control, rainwater and storage tank systems often rely on manual intervention or basic float switches.
This can lead to common problems such as:

pumps running dry
tanks being overfilled
unnecessary water waste
lack of protection during faults
unreliable or unpredictable operation

A control system introduces defined logic and protection, allowing the system to respond correctly to changing water levels and operating conditions.

Typical functions of the control system

A rainwater harvesting controller may provide:

tank level monitoring
automatic start/stop of equipment
pump isolation and protection
timed or conditional water top-up
fault detection and safe shutdown

The exact behaviour depends on how the system is configured and installed.

Two application types: Garden use and Mains water top-up

Rainwater harvesting control systems are typically used in two different scenarios.

Understanding the difference is important, as the requirements are not the same.

1) Garden / non-mains systems

Garden systems are installations that are not connected to the mains water supply.

Examples include:

garden irrigation tanks
water storage for outdoor use
pump-fed systems isolated from household plumbing

In this case, the control system:

monitors tank level
controls pumps or valves
prevents dry running or overfilling

Additional plumbing safety devices are usually not required, as there is no connection to the mains water supply.

2) Mains water top-up systems

In some installations, mains water is used to automatically top up a tank when rainwater levels are low.

This ensures water availability during dry periods but introduces additional requirements.

Because the system is connected to the public potable water supply, UK Water Regulations apply.

Why mains water systems require special design

Mains water must be protected from contamination.

If rainwater or stored water is incorrectly connected to the mains supply, contaminated water can be drawn back into the household or public water system.

To prevent this, mains top-up systems must not have a direct physical connection between mains water and stored water.

This protection is achieved using an air-gap device, commonly a tundish, compliant with UK standards.

Role of the tundish (air gap)

The tundish is a plumbing safety device, not a control device.

Its primary function is to:

create a visible air gap between mains water and the tank
prevent any possibility of backflow or contamination

A secondary function is to safely divert water in the event of overflow.

The tundish works independently of the controller and remains effective even if valves, sensors, or electronics fail.

What is required for each application type

Garden / non-mains systems typically require:

level sensors (float or probe)
pump or valve control
suitable plumbing for stored water

Mains water top-up systems require:

level sensors
a solenoid valve for mains water
a tundish (air-gap device) compliant with BS EN 13076
installation designed in accordance with BS 8515
work carried out by a qualified installer or plumber

What product we provide

Controller (Electronic control)

This product supplies the control system only.

It provides:

automation logic
low-voltage control outputs
decision-making based on input signals

It does not include:

tundish or air-gap devices
plumbing components
pipework or mains water connections

Important notes on responsibility and compliance

The controller operates based on the input signals it receives.

Compliance with UK Water Regulations depends on correct system design and plumbing installation, not on the controller itself.

Incorrect connection of mains water:

may violate regulations
may damage household plumbing
may result in costly remedial work

The controller cannot compensate for non-compliant plumbing or incorrect installation.

Summary (short version)

This is a rainwater harvesting control system
It manages tank level and controls connected equipment
It supports both garden use and mains water top-up
Mains water systems require additional compliant plumbing (tundish / air gap)
The product supplies control logic only, not plumbing components

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