What to check on a Marine Chlorinator.
A marine chlorinator adds a controlled dose of chlorine to potable water to keep free residual chlorine at a level that suppresses bacterial regrowth, including Legionella, in tanks and pipe runs that can sit stagnant for days. It sits downstream of the water maker or bunkering point and upstream of the distribution tank, and unlike a UV unit it leaves a residual that keeps working as the water travels through the piping, not only at the point of treatment.
What a marine chlorinator does
A marine chlorinator adds a controlled dose of chlorine to potable water to keep free residual chlorine at a level that suppresses bacterial regrowth, including Legionella, in tanks and pipe runs that can sit stagnant for days. It sits downstream of the water maker or bunkering point and upstream of the distribution tank, and unlike a UV unit it leaves a residual that keeps working as the water travels through the piping, not only at the point of treatment.
Main components
Electrolytic (electro-chlorination) cell
Generates hypochlorite on board by passing a current through a brine or seawater solution across titanium electrodes, avoiding the need to store bulk chlorine chemicals.
Chemical dosing pump
A metering pump injects a liquid sodium hypochlorite solution from a day tank at a rate matched to water flow, used where electrolytic generation is not fitted or as backup.
Residual chlorine analyser
Continuously measures free chlorine downstream of dosing and trims the dose automatically, since under- and over-dosing are both faults; too little chlorine leaves bacteria uncontrolled, too much produces taste and odour complaints and disinfection by-products.
Contact tank
Provides enough residence time for the chlorine to react before the water reaches the first tap, since dosing without adequate contact time gives a reading on paper without real disinfection.
Selection and sizing
Dosing capacity is sized on peak potable water demand, not average consumption, so residual chlorine holds up during morning and evening peak draw. Electrolytic cells are sized by daily hypochlorite output and need periodic acid cleaning to remove scale from the electrodes, a running cost worth weighing against chemical dosing's simpler maintenance but ongoing consumable purchase.
Regulations and class
- Potable water quality is covered by flag state and port state health regulations rather than a single IMO instrument; many administrations reference WHO drinking water guidelines for residual chlorine targets.
- Passenger ships operating under public health inspection regimes, such as those following CDC-style vessel sanitation protocols, face stricter documented residual chlorine and Legionella control requirements.
- Class societies notate potable water systems where fitted as an optional class notation, with periodic testing records forming part of the survey.
Typical faults
| Fault | Consequence |
|---|---|
| Electrode scaling in the electrolytic cell | Falling chlorine output despite unchanged current draw |
| Analyser probe fouled or uncalibrated | False residual reading, under-dosing goes unnoticed |
| Dosing pump air-locked or day tank run dry | Unprotected water reaches the distribution system |
| Dead legs in piping bypassing the contact tank | Localised bacterial regrowth despite good bulk residual |
What to look for in a supplier
- Electrode or dosing capacity matched to actual peak demand, not nominal tank volume.
- An analyser with a maintenance and calibration schedule the crew can realistically follow, not one that needs a specialist visit.
- Materials compatible with the specific dosing chemical, since hypochlorite degrades many common plastics and elastomers over time.
A good chlorine reading at the dosing point means little if nobody checks it at the furthest tap on the system; residual has to survive the whole run, not just leave the unit strong.