Definition
A mizusumashi is a dedicated material delivery person who follows a fixed, standardized route on a regular timed cycle to supply parts, materials, and empty containers to production workstations. The mizusumashi’s job is to ensure that operators always have what they need at their stations so they never have to leave their work area to get parts. The role is the logistical backbone that connects supermarkets and parts storage to the point of use on the production line.
Japanese Origin
Mizusumashi (水すまし) literally means “water clearer” and refers to the whirligig beetle (family Gyrinidae), a small aquatic insect that moves rapidly in circular patterns across the water’s surface. The name was adopted at Toyota because the material handler, like the beetle, moves in continuous loops through the factory — circling the same route repeatedly, delivering what is needed and collecting empty containers and kanban cards.
History at Toyota
The mizusumashi role developed as Toyota refined its just-in-time system. In traditional manufacturing, operators either fetched their own parts (creating motion waste and inconsistent supply) or parts were delivered in large batches by forklift (creating inventory waste and requiring floor space for storage). Neither approach supported one-piece flow or takt-based production.
Toyota’s solution was to create a dedicated role — the mizusumashi — with a standardized route, a fixed cycle time, and a specific sequence of stops. The mizusumashi typically uses a small towing cart (tugger) rather than a forklift, pulling a train of small carts through narrow aisles on a predictable schedule. This approach delivers small quantities frequently rather than large quantities infrequently, directly supporting the just-in-time principle.
How It Actually Works
The route is standardized. The mizusumashi follows the same path through the factory every cycle. The route is designed to minimize travel distance while serving all required delivery points. It is documented as standardized work, just like any operator’s job.
The cycle is timed. The delivery cycle is typically 20-60 minutes, depending on the factory layout and consumption rates. The cycle time is designed so that parts arrive before operators run out but not so early that excess inventory accumulates at the workstation.
The process on each cycle:
- Collect returned kanban cards and empty containers from workstations
- Bring empties and kanban cards to the supermarket or parts storage
- Pick the parts indicated by the kanban cards in the exact quantities specified
- Load parts onto the delivery cart in route sequence
- Deliver parts to each workstation, exchanging full containers for empty ones
- Repeat
The connection to kanban: The mizusumashi is the physical link in the kanban loop. When an operator consumes parts, the kanban card attached to the container is placed in a collection box. The mizusumashi picks up these cards, which authorize the withdrawal of replacement parts from the supermarket.
Common Mistakes
Using forklifts instead of small carts. Forklifts deliver large quantities, require wide aisles, create safety hazards, and encourage batch delivery. The mizusumashi system uses small carts that fit in narrow aisles and carry only what is needed for the next cycle.
Not standardizing the route and cycle time. If the mizusumashi delivers on an ad hoc basis — going wherever the loudest request comes from — the system degrades into a reactive firefighting operation. The route and schedule must be fixed and treated as standardized work.
Overloading workstations with inventory. The goal is to have exactly enough parts at the workstation to last until the next delivery cycle, plus a small buffer. Delivering more than needed defeats the purpose and creates the same inventory waste the system was designed to eliminate.
Treating mizusumashi as a low-skill role. The mizusumashi must understand the kanban system, know the part numbers and locations, maintain the delivery discipline, and surface problems (parts shortages, quality issues, container damage) as they encounter them. It is a role that requires training and reliability.