“You can live three weeks without food, three days without water, and three minutes without air.” – anonymous
“If you have water you have 1000 problems. If you don't have water you have 1 problem.” – anonymous
“…you really appreciate every drop of water if you have to schlep it.” – gcal1)
Water is critical for life, especially in hot/dry areas like deserts.
Vandwellers living minimally (no showers or slip-n-slides) will typically require 1 gallon of potable water every day for drinking, and 1 additional gallon for cleaning, hygiene, cooking, etc.
drinking water has the highest requirements since it is typically consumed untreated and at room temperature.
It is safest to start with known-drinkable water from public or commercial sources. It is possible to disinfect suspect water by several means; it is not practical to purify water that is chemically or minerologically tainted.
When possible, multiple approaches should be used on the water. The first step in any disinfection routine is to clarify the water to remove haze or foreign matter. Much sediment can clear itself to the bottom if allowed to rest; pour or siphon off the top and leave the sediment behind.
Strain from coarse to fine: through a strainer then a coffee filter, for example.
Heat is an effective way to kill waterborne pathogens. Note that not all pathogens that survive heat treatment are found in water:
Sterilisation of water (killing all living containments) is not necessary to make water safe to drink. For example, boiling may not be effective against bacterial spores such as Clostridium which can survive at 100°C (212°F), however, as Clostridium is not a waterborne enteric (intestinal) pathogen, ingestion will not cause infection.
All waterborne enteric pathogens are quickly killed above 60°C (140°F), therefore, although boiling is not necessary to make the water safe to drink, the time taken to heat the water to boiling is usually sufficient to reduce pathogens to safe levels. Allowing the boiled water to cool slowly will also extend the exposure of waterborne enteric pathogens to lethal temperatures. Boiling also gives a simple visual indicator that a high enough temperature has been reached when a thermometer is not available.2),3)
Typical times at temperature:
Given that information, solar ovens or similar devices that can hold 140F-160F for long periods may provide unpowered heat disinfection. Also see SODIS below.
Chemical treatments require no power making them especially useful offgrid. Treated water can be run through a charcoal filter (Brita) after treatment to improve flavor. Pouring treated water energetically from container to container may allow chemicals to outgas.
The most famous treatment is chlorine bleach. For these purposes, unscented cheap bleach is better than $$$ bleach with additives. It is used at 8 drops/gallon of 6% bleach (6 drops of 8.25% bleach6) and then wait 30 minutes.7) Note that bleach purfication does not reliably kill Cryptosporidium. Increasing wait time to 45mins will kill norovirus and giardia.
Iodine tablets were popular with hikers in the past but impart a noticeable flavor to the water. Some come with an additional tablet to be used after the waiting period, intended to remove iodine flavor and color from the water. Iodine treatment should be avoided by people with shellfish allergies.8)
Hybrid chlorinating-flocculating chemicals such as Flo-Chlor show promise for turbid water, but they are not widespread yet. Flocculation means suspended particles are drawn together and either drop out of suspension or (less commonly) float to the top.
Mechanical filtration has become more common and less expensive. Straw-like personal filters are now sold, for example.
The main drawback of filtration are clogging (addressed by adquate pre-filtration) and relatively slow filtration rate. Look for filters that can be gravity fed so the filtration time isn't tiresome.
Note that filtration through layered fabric is much better than nothing. In India, for example, researchers found:
a filter made of four layers of worn cotton material held back more than 99 percent of all cholera bacteria - using more layers or newer cloth slowed water collection too much.13)
Both saris and coffee filters have about a 20-micron pore size:
Typically coffee filters are made up of filaments approximately 20 micrometres wide, which allow particles through that are less than approximately 10 to 15 micrometres14)
The best we should assume for with such ad hoc filtration is a pathogen reduction. Combination with SODIS (below) might be useful.
SOlar water DISinfection (SODIS) uses sunlight to improve water quality.15) It relies on minimal solar heating of the water, then ultraviolet irradiation in the container. Since UV does not travel far in water, relatively small bottles of 2L or less are used.16) Bottles should be clean and free of surface scratches.
Efficacy: at 86F water temp, ~6 hours of sun (less than 50% cloudy) will significantly reduce diarrhea reduction-causing pathogens in the water. The actual spect is 500w/m2, which is half of the lab spec for solar panel output (1000w/m2) In fully clouded conditions it takes two full days for disinfection to occur. SODIS at normal temperatures might best be thought of as an adjunct method to be used alongside other methods rather than a disinfection method unto itself.
Optimal function may be found by placing small-diameter bottles in a solar oven. This will enhance UV collection and heating.
Water for cooking has lower requirements for biological purity because the water is usually boiled during preparation (see above).
Washwater (non-sewage waste water) is usually stored in a gray tank for later handling.