Dean took on 60 gallons at a dock in Sint Maarten, tasted nothing wrong with it, and had two of his four crew flat on their backs by the second night out of the anchorage. Nobody was in real danger. The watch schedule fell apart anyway, and a 900-mile leg that should have been pleasant became a fortnight nobody wanted to talk about afterwards. Here is the argument, stated plainly, before any gear gets discussed: on a boat, a small treatment stage sitting between the source and the tank costs less and fails less often than boiling or dosing every litre after the water is already aboard. Compact water filtration systems built for marine, RV and field use bring a marina hose and a rain catch to the same drinkable condition, which is the whole reason for putting one in the line. That is not exotic equipment.
A Dock Hose Carries What The Marina Cannot See
Clear water tells you nothing. A hose that looks clean, tastes of nothing and comes out of a tidy standpipe can still carry bacteria, viruses and protozoa, because none of them are visible and most cannot be detected by taste. State that outright, because sailors reason backwards from appearance to safety all the time, and the reasoning does not hold. The case I see most often on deliveries is not the filthy-looking tank at all. It is the boat that sat on a mooring for three weeks in August with 40 gallons of old dock water in it, and a warm half-full tank in the tropics is a science experiment. For any source nobody is testing on your behalf, the closest thing to a rulebook is the EPA’s guidance for private wells, which recommends testing every year for total coliform bacteria, nitrates, total dissolved solids and pH, and testing more often when vulnerable people are drinking it. Then the part that matters most on passage. If a crew member develops severe or bloody diarrhoea, or shows signs of dehydration, get medical advice by radio or phone rather than pushing more fluids and hoping it passes.
Boiling And Tablets Both Cost You Something
Boiling works. It also spends propane you carried from a fuel dock that may be four days behind you, and it spends time on a two-burner stove in a cabin already sitting near 90 degrees. Bring a gallon to a rolling boil, hold it a minute, then wait for it to cool enough to pour into a jug. Repeat five times a day. Tablets are lighter, cheaper and indifferent to weather, but chlorine dioxide wants half an hour to work, longer against cryptosporidium, and the crew tastes it in the coffee for a fortnight. Neither method does anything about sediment, rust flakes, or the smell of a tank that needs scrubbing rather than dosing.
Comparing Treatment Options On A Small Boat
Every option aboard trades away either time, power, weight or taste, and the honest way to choose is to decide which of those four you have the least of. On a 42-foot cruiser with a 90-gallon tank, weight is rarely the binding constraint. Time and propane usually are.
Example scenario: onboard treatment options on a 42-foot cruiser, qualitative ranges rather than measured figures.
| Method | What It Addresses | Time Per Gallon | Onboard Cost Or Draw |
| Boiling on a two-burner stove | Bacteria, viruses, parasites | 15 to 20 minutes with cool-down | Roughly a pound of propane per 5 gallons |
| Chlorine dioxide tablets | Bacteria and viruses, slower on parasites | 30 minutes of waiting | Cents per gallon, plus lingering taste |
| Inline filter at the deck fill | Sediment, chlorine, taste | Fills at dock hose speed | No power draw, one cartridge a season |
| Gravity carbon jug | Taste, sediment, some bacteria | 20 to 30 minutes unattended | No power draw, replaceable element |
| Micro-filtration with a UV stage | Bacteria, viruses, parasites | About a minute a gallon | Small 12-volt draw while running |
An inline filter at the deck fill is the cheapest useful thing on that list, and it is the one most boats already have. It catches grit and knocks down chlorine so the tank stops tasting of a swimming pool. What it does not do is give you any log reduction against a virus, and no cartridge that fills at hose speed ever will. A gravity jug is the opposite trade: patient, silent, no plumbing, and useless when four people want water at once during a squall. Units that pair micro-filtration with an ultraviolet stage sit at the other end, because filtration handles the sediment and protozoa while the UV lamp deals with what slips through, and case-mounted versions of that pairing run near a gallon a minute off a 12-volt feed. They cost more up front than anything else here. They also stop the argument about whether this particular dock, this particular rain catch or this particular island tap is trustworthy, which is worth real money on a two-week passage where you refill twice from sources you have never seen before. Here is the rule I give people. If you fill only from municipal water in marinas you know well and your tank gets cleaned on a schedule, an inline filter and a chlorine residual is enough. If the source changes every few days, treat at the point of use and stop auditing sources you cannot audit.
See also: Smart Business Projection 4079466142 Expansion Dynamics
One Passage Worked Through The Numbers
Run it for a real trip: four aboard, 14 days, and figure 1.5 gallons per person per day for drinking and cooking. That is 6 gallons a day and 84 gallons over the passage, which is most of a 90-gallon tank. Boil all of it at roughly a pound of propane per 5 gallons and you burn about 17 pounds, or two bottle refills at $28 each, so $56 in fuel plus close to 5 hours standing over the stove in the heat. A fortnight of tablets at 40 cents a gallon comes to $33.60, no propane at all, and a chemical aftertaste in everything. A pump-fed unit rated near a gallon a minute clears the same 84 gallons in about 90 minutes of total running time, with no consumable cost on that passage at all.
The stove and the tablets are cheaper than a purifier on any single trip, obviously. What the arithmetic leaves out is the day of a sick crew, the watches somebody else stood, and the 20 gallons you did not treat because you got tired of the routine. That last one is the actual failure mode, and it shows up on the third day, every time.
The Setup Cruisers Settle On Eventually
Most long-term cruisers land in the same place: filter at the fill, treat at the tap, and stop trusting sources entirely. Scale that thinking up and it is the same logic relief agencies work under, because water you cannot have delivered has to be made where you are standing. UNICEF’s Gaza water, sanitation and hygiene update reported in May 2026 that of 633 trucks dispatched from Egypt, only 280 were able to offload across May and June, about 44 percent. A boat is a much smaller supply chain with the same weakness. Which is why water filtration systems sized for a cockpit locker keep ending up aboard boats whose owners swore they would just boil it, and why the crew that arrives rested is usually the one that stopped negotiating with dock hoses somewhere back in the first season.
