Water and Sanitation

How the water and sanitation chain works

Fresh water from the water maker or a supply boat goes into potable water tanks. A treatment train then disinfects it with chlorine dosing or UV, and remineralises desalinated water so it stops attacking pipework. The treated water feeds the cold circuit and the calorifiers, which heat and store hot water for cabins, galley and laundry. Toilet waste travels through vacuum or gravity piping to the sewage treatment plant. Grey water from showers and basins usually drains by gravity on a separate line.

Configurations

• Vacuum toilet systems. A vacuum generator holds the pipework below atmospheric pressure, and each toilet has a discharge valve that opens briefly on flush. The generator is a vacuum pump with a collection tank, a liquid ring pump, or an ejector unit that combines vacuum and discharge. Evac and Jets are the best-known makers.
• Gravity toilet systems. Simpler, but the pipes need continuous fall and the flush uses several times more water.
• Calorifiers. Electric, steam or heat-recovery heating in a stainless or lined steel pressure vessel.
• Potable water treatment. Chlorine dosing units, UV sterilisers, filters and rehardening units.
• Sanitary units. Prefabricated wet units with toilet, shower and basin, built to drop into a cabin.

Key specifications

Standards and what they require

• ISO 15748-1 and -2. Planning, design and calculation of potable water supply on ships and marine structures, including tanks, treatment and distribution.
• WHO Guide to Ship Sanitation. Disinfection practice and Legionella control, with hot water stored at 60 °C (140 °F) or above, returning at 50 °C (122 °F) or above, and cold water kept below 25 °C (77 °F).
• Materials in contact with drinking water. Look for approvals such as NSF/ANSI 61 or WRAS on pumps, valves, linings and hoses.
• Class rules for pressure vessels. Calorifiers need design approval, a hydrostatic test record and certified safety valves.
• MLC Standard A3.1. Where the flag applies it, at least one toilet, one wash basin and one tub or shower for every six persons or fewer without individual facilities.
• MARPOL Annex IV. The toilet system must deliver to an approved treatment plant, comminuting and disinfecting system or holding tank.

Failure modes and inspection

• Vacuum leaks, found by isolating sections and timing the pressure rise.
• Worn discharge valve membranes and seals, the main wear part of any vacuum toilet.
• Urine scale in vacuum pipework and valves, cleared by acid flushing.
• Liquid ring and ejector pump wear, checked against running hours and delivered vacuum.
• Calorifier internal corrosion, sacrificial anode loss and safety valve condition, checked by internal inspection and a hydrostatic test.
• UV lamp hours, fouled quartz sleeves and a drifting intensity sensor.
• Chlorine dosing pump diaphragms and the residual analyser calibration.

Documentation

Ask for the system manual, the vacuum generator's running hours and service record, valve and membrane replacement history, calorifier drawings, pressure vessel certificate and safety valve certificates, materials approvals for drinking water parts, and disinfection records.

Integration with your unit

Vacuum piping can run uphill for short lifts, which frees cabin layouts, but the generator must be sized for the total pipe volume and the number of toilets. Gravity toilets cannot connect to a vacuum line, because a gravity bowl has no discharge valve to hold vacuum. Check that the toilet system's discharge suits your treatment plant's inlet. Match calorifier heat input to the available electrical load or steam supply.

Refurbishment and recertification

Vacuum toilet systems refurbish well, because the makers sell standard kits of valves, membranes and pump parts. A used calorifier needs an internal inspection, a hydrostatic test and recertified safety valves before service. Anything that has held drinking water needs flushing, cleaning and disinfection before reuse, which is why unused surplus is the safer buy for potable water parts.

Water production is under water makers and purification, and treatment of collected black water is under sewage treatment plants.