“You’re going to Tuamotos for almost two months? That’s amazing. We can only go for two weeks, since we have no watermaker,” remarked our friends on a catamaran. Fresh water is unavailable in the Tuamotos. Since they are low-lying atolls, all the underground water is briny. There is no “tap water”. The Tuamotans collect limited rainwater for their washing needs, and purchase drinking water in 5 gallon jugs which are shipped from Tahiti. How do we know if we’ll have enough water for two months in the atolls?
Warning: this post is heavy on numbers… get ready to learn about H2O math!
Aboard our sailboat Aldebaran we have a small watermaker – it is capable of making 1.5 gallons per hour. Check out the photo at bottom to see what it looks like. Due to its small size, it isn’t quite enough to keep up with all our water needs. In comparison, larger sailboats with generators have watermakers producing 10-20 gallons per hour. Some of those folks even have washing machines aboard! The downside of those systems is that when the generators aren’t working (which is the most common problem other boats have) then they can’t make any water at all.
Our lil’ watermaker covers our basic drinking needs and has the added benefit of being the only watermaker in the market that has a manual override (it normally runs on the boat’s 12v system). That way, if our electrical system fails, we can still make water to survive. Perhaps you have to pump feverishly to make water, but at least it’s an option!
Our watermaker may have a small output, but it is very efficient: it uses only 5 amps of power. This is the same as our fridge, or one bilge pump. However when you run the watermaker 8 hours continuously, that consumes 40 amp hours of power. This is about 1/6 of our battery capacity. During an average partly sunny day, about two 100 watt solar panels will produce power to cover that power usage.
How much water does our boat need daily? During the last few years aboard Aldebaran, we’ve seen an average use of 1.5 gallons per person per day. This breaks down to 1/2 gallon drinking water, 1/2 gallon cooking use, and 1/2 gallon washing & light fresh rinse after taking a salt water shower.
Can’t we just leave the watermaker running? No, because it must be monitored and drained every hour, and it can only be run when water conditions are very clean. Typically we only operare our watermaker when more than a mile offshore. In the Tuamotos we’ll have to run it at anchor to keep up with our water needs. But if we are near other boats that might spill oil or gasoline, or there is sediment /pollution in the water, we don’t run our watermaker to preserve the life of the membrane (this is the heart of the system’s reverse osmosis).
If we run our watermaker an average 4 hours per day – which is a realistic average over time – we will make 6 gallons per day. With six crew members onboard, we use 9 gallons per day. Therefore we are depleting the water tank at a rate of 3 gallons per day. This means that our 140 gallon water tank will be depleted in 45 days. In order to stay two months, and make up the difference, we are hoping to capture at least 50 gallons of rainwater with our catchment roof. This is not guaranteed since we’re in the dry season.
In Nuku Hiva, we filled the boat’s water tank at Hoomi, about two hours motoring east from the town of Taiohae. We heard the valley of Taipivai has the best spring water in the south coast of the island, so we anchored Aldebaran and took the skiff to shore where the spring water faucet was located. As usual, there was no dock to moor the sailboat; in fact, believe it or not, the last dock we saw was 12 months ago in Costa Rica!!
We fill three 5 gallon water jerry cans and 3 clean buckets with the spring water faucet and haul back on our shoulders to the skiff; then we haul them back to Aldebaran and syphon it all into the tank. 5 gallons of water weighs about 35 pounds– it gets heavy quickly! We repeat this for several more trips until our 140 gallon water tank is full; it takes about 2-3 hours of non stop work.