Article by ONBOARD Magazine
The right fresh and service water
production and supply can be as unique
as the yachts themselves. Tom Logisch
describes the basics you must consider
Just like energy, the correct design and positioning of the
drinking water supply and wastewater disposal systems
is often a complex matter.
• Where should the drinking and service water come from?
• What will the daily requirement be?
• How big should the water tanks need to be?
• Where is the wastewater disposed of?
1. Where does the water come from
While fixed houseboats are often connected to a drinking water pipe, a yacht can rarely be permanently connected plus, almost all water pipes at the jetties are shut down in winter due to the risk of frost. Therefore you have to provide either large storage tanks or a drinking water treatment system that can also produce the service water at the same time. The water requirement must therefore be delivered by suitable storage tanks or watermakers.
2. Determine the daily requirement
The main water consumers are showers, washing machines and toilets and on occasion bathtubs, with less water needed for drinking and cooking purposes. The first distinction between service water and drinking water comes here: while the toilet and washing machine can be operated with service water, the kitchen, bathroom and shower must have drinking water connections.
Strictly speaking, the water pipes at the jetties are rarely tested for drinking water which means it is a necessity to have your own onboard supplies for the kitchen and bathroom areas. We therefore recommend providing two water tanks; one for the toilet and washing machine and one for the service, kitchen and of course drinking water.
The daily requirement can be roughly determined:
• 5 x toilet per person / day x 3 litre flushing water (marine toilet)
• 2 x 20 litre washing machine per week per person
• 5 litre drinking water for cooking / drinking per person / day
• 20 litre shower water per person / day
A 12 person yacht therefore needs at least 1500 litres of service water and 2100 litres of drinking water per week and of course not to forget the eight plus crew members which equals another 2400 litres of overall water, but these are the lower limits – much more is often used. In order to be self-sufficient for several days, at least two tanks of 2400 litres would be useful.
3. Design of the water supply
We recommend the following design:
• 200 litre service and 200 litre drinking water tank volume per person on board
• Inlet of the raw water via a sea valve at least 30cm below the water line
• Water supply via drinking water supply system, which also generates the service water
• Design in 24 volt on-board voltage, then you don’t need an extra inverter and you are independent of the generator
• Pressure pumps with approx. 20 litres / min and at least 3.5 bar
4. Sewage disposal on yachts
Just like drinking water, wastewater must also be treated accordingly. According to the IMO guideline, the discharge of faecal wastewater into the oceans is prohibited within the 12 nautical mile zone – therefore, appropriately large sewage tanks or a wastewater treatment plant must be provided. These systems are now available in different designs and sizes; always tailored to the number of people on board. The corresponding approval according to the IMO resolution must be observed. Most modern wastewater treatment systems are now available as membrane filter systems or in a fully biological version. The fully biological enteron systems we offer are also suitable for yachts with a maximum of 12 people on board.
We understand each yacht is unique, so contact us for a tailor made design and quotation.
For more details Tel: +49 33203 71501
or visit www.tomlogisch.com