How to save money and energy on water disinfection

Dec 01, 2021
A medium size ship with less than 100 passengers can save around 18 000 USD every year with a smarter disinfection system. This system also removes the need for water bottles, which can save you around 24 000 USD every year with 50 passengers.
A medium size ship with less than 100 passengers can save around 18 000 USD every year with a smarter disinfection system. This system also removes the need for water bottles, which can save you around 24 000 USD every year with 50 passengers.

Why do we usually heat water tanks to 65°?

Usually, ships keep hot water tanks above 65° to prevent Legionella infestations. Legionella is a bacterium that is always available in any source of water. The bacteria spread through small droplets which can be ingested by people nearby the water, for instance when taking a shower. Consequently, they can contract Legionnaires’ disease or Pontiac fever. Compared to COVID-19 for instance, the mortality rate for Legionnaires’ disease is way higher. 10 % of healthy people die and the rate increases for elderly and people with underlying diseases. 

How do we prevent the bacteria from growing?  

There are numerous conditions that increase the risk of Legionella bacteria in water systems. Firstly, the bacterium enjoys temperatures between 20 and 45 degrees. Therefore, the standard recommendation in the UK for instance is to maintain hot water temperature in pipes and tanks above 55 degrees.  Moreover, the presence of biomass and stagnating water provides a suitable environment for the bacteria.

Most ships today only use temperature control to prevent Legionella growth. This requires a large amount of energy, especially if the water is pumped in a closed loop in order to reduce water consumption. A study by E. Cloutman-Green et al. (2019) showed that lowering the water temperature from 65 to 45 degrees resulted in a reduction of over 33 % in annual energy use. 

But surely lowering the temperature increases the risk of Legionella? 

E. Cloutman-Green et al. concluded that a proper water disinfection system does not need temperature control. In their study, there was not found any Legionella bacteria in the system that dosed biocides into the water at temperatures below 55 degrees. The biocides eliminate the biomass, which the bacteria need in order to grow. We provide this system for ships with automatic surveillance which ensures safe potable water on board. As a result, the cold water can be used for drinking water and there is no longer a need for water bottles. 

How much can you save by no longer using a temperature regime?

Suppose we have a circulation pump of 1500 liters per hour, which is standard for a medium-size ship with less than 100 crew members. Also, assume that the ship uses a temperature regime with hot water heated up to 60 degrees. Since the temperature around the water pipes is substantially lower, the water will lose around 10 degrees every circulation. Now, suppose that the ship no longer cares about a temperature regime and heats hot water to 47 degrees. Now, the water will only about four degrees every circulation. This might seem like a minor decrease, but since it takes around 17 liters of diesel every day to maintain one degree loss you can save vast amounts of money every day. Lowering the temperature from 60° to 47° can actually save you around 18 400 dollars every year!

What should you do instead of disinfecting with a temperature regime? 

The Waterworks biocide treatment ensures pure, potable and Legionella free water with a digitally monitored system. And on top of that, you will be able to save a lot of money in the long run. A one-time investment of 27 000 USD is required for installation, and a maximum of 4 400 USD for yearly maintenance. However, as see from the graph in initial graph, the investment pays off after only two years. The graph illustrates the net present value of the two options 10 years into the future. While a temperature regime has a total cost of 142 000 USD, you can save 57 % over the course of ten years by choosing Waterworks, which means a total cost of 61 000 USD. 

But what about plastic water bottles?

Waterworks eliminates the need for drinking water bottles, which has proven to be costly at sea. 1 liter of water can cost up to 0.50 USD, and that quickly adds up for ships with many crew members. Assuming that one crew members needs three liters of water every day and works 320 days a year, it means that installing the Waterworks system pays off from year one! You can read more about our service or contact us for more information. 


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