Module 35 Fresh Water Systems Infographic
Source-to-tap fresh-water production, treatment, storage, distribution and Chief Engineer control crib sheet.
Module purpose
A Chief Engineer level fresh-water crib sheet built around oral-report style questioning. It links machinery operation to potable-water legal control, hygiene, monitoring, records and emergency response.
Navigation
System visuals
Use these visuals for the HTML recap sections: flash evaporator, RO, treatment methods and tank/bunkering controls.
Module 35 • Section 1
1. Oral Framework - Source to Tap
Chief route
Do not stop at the generator. Explain source selection, plant protection, quality proof, treatment, storage, distribution, monitoring and corrective action.
Exam trigger
Recent Chief reports asked about RO plant maintenance, steriliser limits, FW production/distribution, regulations and tank cleaning.
Evidence
Use logs, salinity/conductivity, chlorine/pH, weekly checks, sampling, tank entry, hose disinfection, calibration and corrective action records.
Module 35 • Section 2
2. Flash Evaporator / Fresh Water Generator
Principle
Vacuum lowers boiling point so jacket water or waste heat can flash part of the feed into vapour. Vapour condenses as distillate; brine is rejected.
BTT
Brine top temperature is the highest brine temperature in the evaporator. Higher BTT can improve output but increases scaling and carryover risk.
Protection
Clean intake, demister, brine removal, anti-scale dosing, salinity monitor and dump valve prevent contamination of potable tanks.
Module 35 • Section 3
3. Reverse Osmosis
Osmosis
Water naturally moves through a semi-permeable membrane from dilute to concentrated solution.
Reverse
High pressure overcomes osmotic pressure so water passes as permeate while salts remain in concentrate.
Maintenance
Pretreatment, antiscalant/pH control, dechlorination as required, pressure/DP/flow/recovery and conductivity trends protect membranes.
Module 35 • Section 4
4. Treatment and Stabilisation
Chlorine
Provides residual disinfection through tanks and pipework. Around 0.2 ppm at the far point is a practical target where specified by the ship plan.
Mineralisation
Restores stability to very soft produced water, typically calcium hardness and bicarbonate/alkalinity, sometimes magnesium depending on system.
Alternatives
UV gives point treatment with no residual. Silver ion gives antimicrobial residual but requires dose monitoring. Thermal disinfection is for recovery/legionella control.
Module 35 • Section 5
5. Tanks, Maintenance and Bunkering
Weekly
Food and drinking-water supplies should be inspected at least weekly and recorded.
Tank maintenance
Six-monthly pump/hosing/rotation; annual open, inspect, clean/disinfect; pressure test not exceeding five years, flush and sample.
Bunkering
Approved source, dedicated capped potable hose, flush to waste, controlled loading, prevent backflow/cross-connection, monitor residual/pH and record.
- Dedicated blue/marked potable hose
- Flush first water to waste
- Prevent overflow, backflow and wrong tank filling
- Monitor residual chlorine and pH
- Sample and record source, quantity and tank
- Trend results rather than relying on one good reading
Module 35 • Section 6
6. Unsafe Water Response
First priority
Protect people: isolate suspect supply, provide alternative drinking water and escalate to Master/company/medical guidance.
Investigation
Sample, trend, check source, plant, tanks, residual, pH, conductivity/chloride, treatment and dead legs.
Return to service
Clean, disinfect, flush, verify with satisfactory testing and record corrective action before returning the system.