How to Build a Rainwater Harvesting Control System (DIY)

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Components Overview (DIY Assembly)

This section explains the main components of a rainwater harvesting control system, their role, and how they work together when assembled.

The control unit provides logic and automation.
All plumbing and hydraulic components are supplied separately.

1️⃣ Rainwater Storage Tank

Purpose:
Stores collected rainwater or other non-potable water for later use.

Notes:

Can be above-ground or underground
Size depends on application (garden, irrigation, household use)

Search terms:

rainwater storage tank
water storage tank

2️⃣ Level Sensor (Tank Level Detection)

Purpose:
Detects the water level inside the tank and provides feedback to the controller.

Common types:

Conductivity level probe (solid-state, no moving parts). Not suitable for our controllers
Float switch (mechanical on/off level detection)
Non-Contact Level Sensor (capacitive, mounted outside the tank)

Which is best for you by following link: Water-level-indicator (opens in new window)

Role in the system:

Signals when water level is low
Signals when the required level has been reached

Search terms:

water tank level sensor
conductivity level probe
float switch level sensor

3️⃣ Rainwater Top-Up Controller (Control Unit)

Purpose:
This is the control logic of the system.

What it does:

Receives signals from level sensors
Decides when to enable or stop water top-up
Controls solenoid valves and optional pumps
Applies timing, delays and safety logic

Important:
This unit does not handle water directly.
It controls other components electrically.

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4️⃣ Solenoid Valve (Mains Water Control)

Purpose:
Allows mains water to enter the system when commanded by the controller.

Key characteristics:

Normally closed (fails safe)
Suitable for potable water
Electrically controlled

Role in the system:

Opens only when the controller requests top-up
Closes automatically when level is restored

Search terms:

WRAS approved solenoid valve
potable water solenoid valve
BSP solenoid valve

5️⃣ Air Gap Tundish (Mains Protection Device)

Purpose:
Provides a physical air gap between the mains water supply and stored water.

Why it is required (mains systems only):

Prevents backflow and contamination
Required under UK Water Regulations
Protects the potable water supply

Important:
The tundish is a plumbing safety device, not part of the controller.

Secondary function:

Safely diverts overflow if a fault occurs

Search terms:

air gap tundish BS EN 13076
rainwater harvesting tundish
mains water air gap device

6️⃣ Optional Pump

Purpose:
Supplies water from the storage tank to the end application.

Role in the system:

Operates only when sufficient water is available
In case when need transfer rain water from water collectors to main non-potable water tank
Can be isolated during mains top-up if required

Search terms:

rainwater pump
submersible water pump
pressure pump rainwater

7️⃣ Plumbing and Pipework (Not Supplied)

Includes:

Pipe connections
Valves and fittings
Drain and overflow routes

Responsibility:
All plumbing work must be designed and installed by a competent installer.

How the System Works (Summary)

The level sensor monitors the tank water level
The controller evaluates the level condition
When the level is low, the controller opens the solenoid valve
Mains water flows through the tundish air gap into the tank
Once the target level is reached, the valve is closed
The system returns to normal operation

Important Notes for DIY Installations

The controller provides logic and control outputs only
Mains water connections require compliant plumbing design
The tundish is essential for mains top-up systems
Incorrect installation may cause regulatory non-compliance or system damage

Summary

This system combines:

Electronic control (controller)
Level sensing (sensors)
Hydraulic safety (tundish)
Controlled water supply (solenoid valve)

Each component plays a specific role, and correct assembly ensures safe, reliable and compliant operation.