A fresh water module, also called a potable water module, provides clean, warm water regardless of location. In this article, we explain exactly what a fresh water module is used for, how it works, what types are available, and how the term differs from terms such as potable water module, water heater, or water supply system.
Table of Contents
What Is a Mobile Water Supply System?
In the context of hot water generation, the term refers to mobile water heaters such as fresh water modules. These are flexible solutions, independent of time and location, that ensure a reliable hot water supply even outside of fixed installations. They are typically compact, transportable units that can be quickly put into operation at various locations.
What Are Mobile Water Heaters Used For?
Mobile water heaters are versatile and serve as an indispensable temporary solution or supplement in situations where a stationary hot water supply is unavailable or has failed.
| Application Area | Description |
|---|---|
| Emergencies | Bridging the gap in case of failure or maintenance of the on-site hot water supply |
| Construction and Renovation | Supply of construction sites or buildings during renovation and conversion work |
| Events and Trade Shows | Provision of hot water for mobile sanitary facilities, catering, and commercial kitchens |
| Industry and Commerce | Temporary supply during production peaks or special orders |
| Leisure | Mobile pool heating or hot water supply for campsites and temporary accommodation |
The devices can be used as a pure water heater, a potable water station, or a process water station.
How Does a Fresh Water Module Work?
A fresh water module operates on the flow-through principle and is used for hygienic hot water generation. Unlike a classic hot water storage tank, which holds a large amount of water, the potable water station heats the water only on demand.
The functionality is based on a plate heat exchanger:
- Demand: When hot water is requested at a tap (e.g., faucet or shower), cold potable water begins to flow through the plate heat exchanger.
- Heat Transfer: Simultaneously, warm heating water (usually from a buffer tank, which is heated by a heating system or a mobile heating unit) is directed through the heat exchanger.
- Heating: The cold potable water and the warm heating water flow past each other in separate circuits. The heat from the heating water is efficiently transferred to the potable water without the two media mixing.
- Supply: The now-heated potable water is directed straight to the tap. The cooled heating water flows back for reheating. This principle ensures high potable water hygiene, as the water does not stagnate and the risk of Legionella formation is minimized.
Can Water Heaters Be Combined with Mobile Heating Units?
Yes, the combination of a mobile water heater (fresh water module) with a mobile heating unit (mobile heater or heating container) is the optimal solution for an autonomous hot water supply.
Since the potable water station itself does not have its own heat source, an external source for heating water is necessary. Mobile heating units, which can be operated with gas, oil, or electricity, generate the necessary warm heating water. This heating water is directed via insulated hoses to the mobile fresh water module, where it is used in the plate heat exchanger to heat the water.
This combination enables a flexible and powerful hot water supply that is independent of the on-site infrastructure.
Mobile Hot Water Supply Even Without a Buffer Tank
With mobile fresh water modules (potable water stations), a large, separate buffer tank is generally not required.
The reason for this lies in the design of the mobile solution:
- Direct Coupling: The mobile fresh water module is connected directly to the mobile heating unit (mobile heater or heating container). The heating unit takes on the function of the heat generator.
- Instantaneous Water Heater Principle: The fresh water module operates on the flow-through principle. The warm heating water is directed from the mobile heating unit directly through the plate heat exchanger of the fresh water station as soon as hot water is requested.
- No Storage of Potable Water: Since the fresh water module does not store the potable water but only heats it at the moment of demand, a buffer tank for storing the potable water is not necessary.
- Internal Buffering of the Heating Unit: The mobile heating unit itself has an internal water circuit (heating water) that serves as a small buffer to quickly release heat to the fresh water station and keep the temperature constant. The heating unit dynamically regulates the generation of heating water to deliver the required output for hot water generation.
In summary: The mobile heating unit delivers heat on demand to the fresh water module, eliminating the need for a large, stationary buffer tank. The mobile solution is therefore a compact and efficient combination of a heat generator and hygienic hot water generation using the flow-through method.
What Types of Water Heaters Are Available?
Water heaters can fundamentally be distinguished by their function and their energy source.
| Distinguishing Feature | Types | Description |
|---|---|---|
| Operating Principle | Storage Systems (Boiler) | Keep a certain amount of water constantly at the desired temperature; suitable for high, short-term demand |
| Instantaneous Water Heaters (Durchlauferhitzer) | Heat the water only when needed (on demand) using their own, direct heat source; space-saving and hygienic | |
| Fresh Water Stations | Use the flow principle but not with their own heat source, but with heat from a buffer tank or an external heating unit (indirect heating) | |
| Energy Source | Electric | Use electricity (e.g., instantaneous water heaters, boilers) |
| Gas/Oil | Use fossil fuels (e.g., gas instantaneous water heaters, central heating boilers) | |
| Solar | Use thermal solar systems to heat the water | |
| Thermodynamic | Use a heat pump to extract heat from the ambient air |
Water Heater, Fresh Water Station, Domestic Hot Water Station – What Are the Differences?
The terms are often used synonymously but technically describe different concepts of hot water preparation.
| Term | Function | Heat Source | Hygienic Advantage |
|---|---|---|---|
| Water Heater | General term for all devices for hot water generation | Direct (e.g., electricity, gas) or Indirect (e.g., heating boiler) | Variable (storage tanks pose a risk, instantaneous heaters are hygienic) |
| Domestic Hot Water Station | Heats potable water using the flow principle | Indirect: Uses warm heating water from a buffer tank or an external heating unit | Very high, as no potable water is stored (Legionella prevention) |
| Fresh Water Station | Technically identical to the domestic hot water station | Indirect: Uses warm heating water from a buffer tank or an external heating unit | Very high, as no potable water is stored |
| Boiler/Storage Tank | Stores a large amount of hot water | Direct or Indirect | Lower, as stagnant water at insufficient temperatures promotes Legionella growth |
| Instantaneous Water Heater | Heats potable water using the flow principle | Direct: Has its own, usually electric or gas-powered heat source | High, as no water is stored |
Water Heater is the general term. Domestic Hot Water Station and Fresh Water Station are essentially identical terms for a highly hygienic flow system that uses heat from an external buffer. The main difference from a conventional instantaneous water heater is that the station itself does not have its own heat source but merely functions as a heat exchanger. It uses heat from a separate heating circuit (buffer tank or mobile heating unit).
Conclusion
Mobile water heaters, particularly in the form of Fresh Water Modules or Domestic Hot Water Stations, represent a flexible, and hygienic solution for temporary hot water supply. Their central feature is the flow principle using a plate heat exchanger, which allows the potable water to be heated only on demand, thereby minimizing the risk of Legionella formation from stagnant water.
The decisive advantage of the mobile application lies in the direct coupling to an external heat source, such as a mobile heating unit. This combination eliminates the need for a large, separate buffer tank and enables a compact, powerful, and immediately operational hot water supply for emergencies, events, or construction sites.
While Water Heater is the general technical term, Domestic Hot Water Station and Fresh Water Module designate the highly hygienic, indirect flow system, which is clearly distinct from the conventional Instantaneous Water Heater with its own, direct heat source. The mobile fresh water station is thus the ideal choice when flexibility, high performance, and maximum potable water hygiene are required.
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References:
Düsseldorf.de (seen on 10/15/2025). Mobile und zeitweilige Wasserversorgungsanlagen.
Co2online.de (seen on 10/15/2025). Frischwasserstation – Funktion, Nutzen und Kosten.
Energie-Experten.org (seen on 10/15/2025). Frischwasserstation: Technik, Nachteile & Nachrüstung.