Clear water is not the same as safe water: filtration clears out material, while purification deals with what you cannot see, and the two work best together.
Two different jobs
Filtration removes dirt, sediment and some impurities. Purification is the step that makes water safe to drink by dealing with germs. The book is firm that water from rain or other sources is still impure and must be properly filtered and purified before use, and that impurities can include not only dirt but also metals such as copper, iron and arsenic.
The book's three-layer DIY filter
If a shop-bought filter is too expensive or complicated, the book describes a simple filter made in a five-gallon food-grade bucket, with three layers the water passes through: gravel, sand and activated charcoal.
- Drill a hole at the bottom of the bucket with a hole saw and fit a plastic pipe connection through it.
- Cover the outer end of the pipe with mesh netting.
- Inside, build up from the bottom: a layer of gravel, a mesh screen, a layer of sand, another screen, then activated charcoal.
- Pour water in at the top and collect it as it comes out of the pipe, clear of debris and sand.
What this filter does not do
A layered filter like this clears particles and improves taste, but it is not a guarantee that water is safe. It does not reliably remove germs, and it does not guarantee the removal of dissolved chemicals or metals. That is why the book still recommends boiling the water before drinking. Boiling is aimed at germs; it does not remove chemical contamination, and for that you need proper testing and, if necessary, a different treatment.
A sensible routine
- Collect and store water properly (safe water storage practices).
- Filter out sediment and particles.
- Purify before drinking, for example by boiling, or with a suitably rated purifier used as the maker directs.
- Test your water at least once a year, even if it looks and tastes normal.
The staged approach is explained further in our beginner's guide to water filtration and purification.
Worked example: drinking water from a rainwater tank
- Collect from the roof into a covered tank so light and debris stay out.
- Let the water settle and filter out particles first, because treatment works better on clear water.
- Treat for germs before drinking: boil it, or use a purifier rated for microbes and follow the maker’s instructions.
- Have the water tested for chemical and biological quality, because roofing and pipework can affect what ends up in the tank.
- Repeat tests over time and after repairs or flooding. If a result fails, do not drink the water until you have taken advice.
Sources and further reading
- Guidelines for drinking-water quality (World Health Organization).
- Private water supplies (Drinking Water Inspectorate): guidance on private supplies in England and Wales. Ask your local authority’s environmental health team what applies to your supply.
Where the books cover this
Chapter 6, “Water Collection, Filtration, and Purification”, covers how to build a water filter, winter-proofing a water system, and greywater and blackwater management. The same chapter text appears in both books (see the comparison), so you only need one. Some examples use US units and US organisations, so check how they apply where you live. You can read sample pages before buying.
Off Grid Survival for Beginners · The Off-Grid Survival Manual
The whole water chapter is in the Off-Grid Water guide, and the DIY filter build is also set out in The Off-Grid Survival Manual.