RainStick Recirculating Shower System

RainStick is a recirculating shower system for homeowners and sustainability focused builders. It delivers a high-flow shower experience while reducing water and energy consumption by recirculating water through an integrated filtration and UV sanitation system.

The Challenge:

The project with RainStick started as an R&D exercise to define the high level approach to water recirculation, which eventually expanded into a functional prototype and production design. When the engagement began, the core challenge was establishing a system level architecture for a product that did not yet have a physical prototype. Several primary technical requirements had to be met to ensure commercial viability:

Thermal Management: The system needed a validated method for maintaining water temperature at high flow rates while staying within the electrical power limits of a standard residenti
Plumbing Code Compliance: The architecture required precise engineering to manage the separation and mixing of potable and non-potable water according to North American st

Installation Integration: The design needed a comprehensive system level plan to ensure the installation process was manageable for plumbers and electricians in standard residential envir
Water Sanitation: The project scope included defining a functional filtration and sanitation sequence to manage water quality during real time recirculation.

The Approach:

Inertia’s initial R&D focus was on the thermal management system. We constructed a specialized test rig to determine the heater power required to maintain consistent temperatures at specific flow rates. This data showed that an onboard heater would require high power wiring, so we instead selected an architecture that maintains temperature by slowly replacing recirculating water with new hot water from the home’s existing supply.

In the system design phase, we benchmarked potential architectures through full teardowns of existing market products. We prioritized high risk elements, specifically the mixing valve and plumbing code compliance. A major technical unlock occurred when the team identified a cost effective, off the shelf mixing component from a supplier in Spain that provided the necessary functionality. This discovery allowed the project to move forward without the need for a custom designed internal valve.

To address plumbing code requirements regarding the mixing of potable and non-potable water, Inertia designed an innovative two-chamber shower head. This component allowed for two distinct shower modes, using either potable new water or recirculated water, while avoiding backflow. After defining the system operating states and high risk subsystems, we established the remaining physical architecture, including the packaging of all necessary components within the desired space. We eventually built a complete system which was used to tune the control system and achieve the required operating targets.

The Outcome:

The collaboration transitioned the project from a conceptual R&D phase into a functional, low volume production ready design. By the end of the engagement, Inertia delivered a pre-production prototype featuring representative mechanical parts and a control system that met all core functional objectives. This prototype and the associated technical data enabled RainStick to successfully transition to Linamar for full-scale assembly.

Beyond the technical build, the work provided the foundation for RainStick to secure intellectual property and win awards at multiple industry tradeshows. By solving the critical thermal and plumbing constraints through a validated water replacement model, Inertia provided the engineering certainty required for RainStick to move from a theoretical concept to a commercially viable and certified appliance.

Services Provided

Concept Development & Validation

Requirements Definition

Technology Feasibility

User Needs Development

Concept Prototyping

R&D

Prototyping & Rapid Builds

Human Factors & Usability

Industrial Design

Mechanical Design

User Interface Design

Software & Firmware Design

Electronics Design

System Design

Design For Manufacturing

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