Chapter 3
What Is In The Water
"Contaminated" is not one thing. Water problems fall into biological and chemical camps that behave completely differently, and the mistake that hurts people is treating for one while the other goes straight through. This chapter breaks the threats down by size and behavior so you can pick the right method every time.
Biological Contamination
The fastest way untreated water hurts you. Illness that empties you from both ends is dangerous precisely because it dehydrates you in the situation where clean water is already scarce. Assume every surface source is biologically contaminated, no matter how it looks.
Bacteria
~0.2–2 microns
E. coli, Salmonella, Campylobacter, Shigella, Vibrio cholerae, Legionella. Sourced from human and animal waste and warm stagnant plumbing. Symptoms usually arrive within hours to a couple of days.
Beaten by: boiling, chlorine, iodine, chlorine dioxide, UV, 0.2 micron filters, RO, distillation. This is the easy one.
Protozoa & Parasites
~3–15 microns
Giardia and Cryptosporidium above all, plus amoebae and larger worm eggs. They travel as tough cysts, which is why they shrug off chlorine and iodine — Cryptosporidium is famously chlorine-resistant. Beautiful wilderness streams with livestock or beaver upstream are the classic vector, and the illness can drag on for weeks.
Beaten by: boiling, any 0.2 micron or finer filter, UV, RO, distillation. Chlorine dioxide with a long contact time. Not reliably by chlorine or iodine.
Viruses
~0.02–0.3 microns
Norovirus, rotavirus, hepatitis A, enteroviruses. Small enough to slip through a standard hiking filter, and overwhelmingly tied to human sewage — floodwater, failed septic systems, dense camps, and travel abroad. Tiny doses cause illness.
Beaten by: boiling, chlorine, iodine, chlorine dioxide, UV, purifier-rated units, RO, distillation. Not by ordinary 0.2 micron filters.
The practical takeaway: filters and chemicals cover each other's gaps. Filters catch what chemicals can't kill (Crypto); chemicals kill what filters can't catch (viruses). Carrying both is the cheapest redundancy in preparedness — or just boil, which covers all three.
Chemical Contamination
Slower to hurt you and much harder to remove. Chemicals are dissolved, so there is nothing to strain and nothing to kill. Disinfection is irrelevant here — this is carbon, reverse osmosis, distillation, or a different source.
Organic Chemicals, Fuel, and Pesticides
Gasoline and diesel components, solvents, herbicides and pesticides, industrial runoff, and the byproducts of burned plastics after a fire. Activated carbon is genuinely good at most of these — it is what carbon is for — and RO with a carbon pre-filter is better. Heavy petroleum contamination is a "find another source" problem; do not try to filter a fuel sheen. Never draw water downstream of a spill, a burn scar, or a flooded industrial site.
Heavy Metals, Arsenic, and Algal Toxins
Lead from old plumbing and solder, arsenic and uranium from natural geology in well water, iron and manganese (unpleasant but mostly harmless), copper, and mine drainage. Certified lead-rated carbon blocks handle lead; arsenic generally needs RO or distillation. Cyanotoxins from blue-green algae blooms are their own category — they survive boiling and pass most filters, so the only correct response to a visible bloom or surface scum is to not use that water, for people or animals.
Nitrate and Nitrite: The Fertilizer Problem
This is the contaminant most preparedness plans miss, and it is the one that matters most for anyone planning to drink from a fish pond, a stock tank, a shallow well near agriculture, or any water body carrying a heavy natural fertilizer load.
Where it comes from. Fish waste, waterfowl droppings, manure, decaying plants, and commercial or organic fertilizer all release ammonia. Bacteria oxidize ammonia into nitrite, then nitrite into nitrate — the nitrogen cycle every aquarium keeper knows. In a stocked or fertilized pond, that cycle runs continuously and the end products accumulate in the water.
Why it matters. Nitrite interferes with the blood's ability to carry oxygen, causing methemoglobinemia — historically called blue baby syndrome. Infants under six months, pregnant women, and some livestock are dramatically more susceptible than healthy adults. There is no taste, no color, and no smell to warn you. Long-term high nitrate intake also carries broader health concerns.
What does not work. Not boiling — that concentrates it. Not chlorine, not iodine, not UV, not hollow-fiber or ceramic filters, and not activated carbon. Every popular emergency water tool on the shelf leaves nitrate exactly where it was.
What does work. Reverse osmosis, distillation, or anion exchange resin. If a nutrient-loaded pond is a realistic long-term source for you, one of those belongs in your plan — and until you have it, use that water for washing, livestock, and irrigation rather than for drinking, and never for infant formula.
Test, don't guess. Nitrate and nitrite test strips cost very little, read in a minute, and are the only way to know. Aquarium and pond test kits measure exactly the right things. Keep some with your water gear.
The Method-vs-Threat Matrix
One table to keep in your head. Read across your suspected contaminant to find a method that addresses it.
| Contaminant | Boiling | Chemicals | Filter 0.2 µm | Carbon | Reverse Osmosis | Distillation |
|---|---|---|---|---|---|---|
| Sediment & turbidity | No | No | Yes | Partly | Yes | Yes |
| Bacteria | Yes | Yes | Yes (0.2 µm) | No | Yes | Yes |
| Protozoa (Giardia, Crypto) | Yes | Weak (ClO₂ w/ time) | Yes | No | Yes | Yes |
| Viruses | Yes | Yes | Purifier only | No | Yes | Yes |
| Nitrate / nitrite | No (concentrates) | No | No | No | Yes | Yes |
| Organic chemicals, fuel, pesticides | No | No | No | Yes | Mostly | Mostly |
| Heavy metals (lead, arsenic) | No | No | Rated blocks only | Some | Yes | Yes |
| Salt / dissolved solids | No | No | No | No | Yes | Yes |
| Algal toxins (cyanotoxins) | No | No | No | Some | Mostly | Partly |
| Radiological particles | No | No | Partly | Some | Mostly | Mostly |
"Chemicals" means chlorine, chlorine dioxide, or iodine at the correct dose and contact time. Filter ratings assume an intact, in-date element that has never been frozen. "Some" and "Partly" mean it depends on the specific contaminant and on a certified product — carbon only removes lead in blocks certified for it, and no carbon cartridge touches nitrate or salt. When in doubt, treat a "Partly" as a no and step up to reverse osmosis, distillation, or a different source.
Frequently Asked Questions
- What is the difference between bacteria, parasites, and viruses in water?
- Bacteria are single-celled organisms roughly 0.2–2 microns across, like E. coli and Salmonella, and they cause fast-onset gastrointestinal illness. Protozoan parasites such as Giardia and Cryptosporidium are much larger cysts, 3–15 microns, with tough shells that resist chlorine and cause illness that can last weeks. Viruses like norovirus and hepatitis A are far smaller, about 0.02–0.3 micron, so filters often miss them, but they are killed easily by heat and chemical disinfection.
- How do you remove nitrates from water?
- Reverse osmosis, distillation, or anion-exchange resin. Boiling, chlorination, carbon filtration, and standard hollow-fiber or ceramic filters do not remove nitrate at all, and boiling makes the concentration worse as water evaporates away. Nitrate is a particular hazard for infants under six months and for pregnant women.
- Why is nitrite dangerous in fish pond water?
- Fish waste and decaying organic matter release ammonia, which bacteria convert to nitrite and then nitrate. Nitrite interferes with the blood's ability to carry oxygen — the cause of methemoglobinemia, or 'blue baby syndrome' — and a pond with a heavy fish, waterfowl, or manure load can carry meaningful concentrations. It is invisible, tasteless, and unaffected by filtering or boiling.
- Does boiling water remove chemicals?
- No. Boiling only handles living organisms. Non-volatile chemicals, nitrate, metals, and salt are left behind and become more concentrated as steam escapes. Some volatile organic compounds do evaporate, but that is not a reliable treatment. Chemical contamination needs activated carbon, reverse osmosis, or distillation — or a different source.