Water water everywhere. Nor any a drop to drink.
The Rime of the Ancient Mariner- Samuel Taylor Coleridge
Everyone knows consuming sea water is a death sentence and you can only survive a few days without water. So it should be no real surprise that the most common question on the subject of rowing the Atlantic (after ‘are you crazy’) is about getting enough drinking water. It is literally a question of life and death. This blog is therefore about the perils of staying hydrated at sea. Warning it’s going to get a bit sciencey!
If you cast your minds back to the school classroom you may remember ‘osmosis’ the movement of water from a less concentrated solution to a more concentrated solution through a partially permeable membrane, such as the walls of the cells that make up our bodies. It is the key to understanding everything in this blog. A quick google search will bring up a few good YouTube videos! In a nutshell, osmosis will occur to make the concentrations of a solution on each side of a membrane the same.
Drinking Sea Water
So what’s the big deal with drinking sea water? Our bodies contain about 9 grams of salt per litre of water, whereas a litre of seawater contains 35 grams, a much higher concentration. If you drink sea water osmosis will occur as water within your body’s cells moves out of the cells to equalise the concentrations of salt. The water leaving your cells will cause you to become more dehydrated than before drinking the salty sea water. It thus kills you faster than drinking nothing at all.
Getting Drinking Water
During our row we will not be able to drink the sea water nor can we carry enough fresh water on our small boat. Instead we will turn the oceanic water around us into drinking water by extracting the salt. A mechanical box of tricks, colloquially know as a water maker and formally as a seawater desalination system, will do this for us.
The water maker works by reverse osmosis. A pump takes in sea water and pressurises it to about 70 bar (1000psi) using a combination of valves and pistons. This pressure causes the naturally occurring osmosis process to reverse. This high pressure sea water is then channelled past a special membrane that is only permeable to water molecules, whereby a proportion of the seawater(about 40%)passes through the membrane to become drinking water and the remaining seawater (about 60%) becomes more concentrated and is discharged back into the sea. Modern technological advances have seen the evolution of the energy recovery pump, that extracts energy by de-pressurising the water before putting it back into the sea. All in all it requires about 5 watts of energy to make 1 litre of water, that’s the same energy required to fully charge your smart phone. This energy will come from the solar panels and batteries installed on our boat. We will also have a chemical fuel cell if there are a few cloudy days.
The water maker is a complex piece of machinery and its failure is one of the most common causes of teams dropping out, hence the detailed level of research into the topic. Most accounts of ocean rows include a section on the day ‘the water maker broke’. The author will usually rank that day as the worst. To conserve their supply they stop the sweaty and dehydrating business of rowing, sat dead in the water hoping not to become truly dead in the water…..
We as a team will be learning how to fix every part of the water maker and carrying plenty of spare parts. As a back up we will also have hand pumps to desalinate the water, they work in a very similar manner to the main electric water pump but the of energy comes from our already tired arms! As a further back up we will have 300 litres of bottled water in the bottom of the boat. This water also acts as ballast that will ensure our boat selfrights in the event of a capsize, so must be replaced as soon as it has been drunk with salt water then fresh water when everything is working again. In short, we want the water maker that is going to survive the longest, or it’s going to be an even longer journey.
Keeping it all in balance
The point of all this water is to keep us hydrated. Our bodies need water for many processes including transporting nutrients and oxygen, regulating temperature and getting rid of waste products. Research has shown that the losses of 2% of body fluid can reduce mental performance, which can include short-term memory, arithmetic efficiency, motor speed and attention. What is more 75% of muscle cells are water so athletic performance can be reduced by up to 20% by the same 2% loss. We require up to 2.5 litres of water on normal day but as ocean rowers we will need around 12 litres due to the amount we will sweat whilst rowing. We will also sweat out salt which include electrolytes such as sodium, potassium and calcium. These chemicals are essential for the bodies blood chemistry, muscle action and transmission of electrical impulses in our nervous system; without enough electrolytes our bodies will shut down.
This means we cannot just drink the water we have produced as we will not replace the electrolytes lost through sweat. Moreover, drinking excess water will cause the osmosis process to move the electrolytes still within the body to leave the cells and equalise the concentration resulting in further loss of electrolytes. This causes a condition called hyponatremia, also know as water intoxication, which is the reverse of drinking seawater and just as deadly.
Fortunately, sports scientists have been working on the issue of maintaining the correct levels of hydration during sporting events and the product of their efforts can now be purchased in the forms of powders that can be added to plain water to ensure our bodies get all the replacement electrolytes they need.
In summary we will be harnessing the suns energy to take all the salt out of sea water with our water maker. We will then add some salt back in and drink it. I know you as a reader understand the importance of water but I hope having read this blog that you understand the pressure I feel when going out to buy a £5000 water maker later this week!
MEN OF OAR
The Men of Oar Blog has been written to keep you, our supporters, up to speed with our progress through our challenge and inform you about some of the more complex aspects of Ocean Rowing. Although it is based on true events, the blog is written to entertain. We hope you enjoy-if so please share!