The Means of Life :
Water safe to drink is the single most important thing for survival. In the short term, the crisis need can be dealt with by cistern storage, but anything over a week to two weeks is hard to store. From experience during a water strike, the writer recalls that the needs for water for washing and cooking were very real and far exceeded the problems of drinking water. For that reason, it is worth looking seriously at the means for clarifying and sterilising water.
Design Principles for Storage Cisterns :
A cistern is nothing more than a tank, manufactured or improvised, for storing water in, preferably with a lining and cover to keep out contamination and to reduce water loss by evaporation. The following are practicable. :-
- A Plastic Rain Barrel with a lid and a tap (spigot) for emptying water. This holds about 50 gallons (225 litres), or enough for two people for 25 days. Fill in a cris and add about a teaspoon (5 ml) of Milton solution to keep the water fresh.
- A strong box lined with sacking and a strong unperforated plastic bag. The capacity would vary according to the size of the bag, but could be from 10 to 50 gallons.
- Larger cisterns can use building plastic (e.g. Visqueen) or plastic tarpaulin and pond liners, inside a framework of timber, padded steel mesh or staked brick or blockwork.
- The largest improvised cisterns, with capacities of 50 to 400 gallons, can be made by digging a hole and lining it with plastic. The lip of the cistern should be well above local ground level, with drainage gulleys to channel surface rainwater around and away from it. The cistern should be covered against contamination. A properly roofed cistern with earth mounded over it, could even withstand any explosion other than a direct hit.
Raw Water Purification
Given a little care and thought, it is possible to purify most sources of water other than raw sewage and industrial pollution, using fairly simple equipment. The major problems are as follows :-
- Suspended Sediment : This consists of clay particles and organic material. It is removed by a combination of settling, flocculation and filtration.
- Natural Organic Debris : This covers everything from bird-dirt to micro-organisms. This has to be removed further by fine filtration (slow sand-bed or slow clay-bed) and by some kind of sterilisation.
- Dissolved Natural Organic Chemicals : These can be natural ammonia, humic, carbonic and nitrous acids, and other results of natural organic processes. Neutralised by absorbtion into clay, lime and the effects of chlorination.
- Dissolved Industrial Organic and Inorganic Chemicals : These include industrial phenols, analines, benzenes and other petrochemicals. In worst cases, these can include metal salts and cyanides which cannot be removed by expedient means. Very difficult to remove except commercially using zeolite chemicals. Water sources polluted by these can be cleared naturally by slow filtration through reed-beds, but small-scale purification may only be possible by low-temperature evaporation using a solar still.
It is logical to choose a source of water that is already as clear and pure as is possible before processing it further. Water trapped in domestic plumbing can provide up to 100 gallons of good-quality water. Rainwater collected from clean catchments in a wet climate can be a good source; rainwater from roofs and guttering can be contaminated with rust, soot and bird dirt. Streams may be contaminated by grazing animals, farm slurry, sewage system discharges and waste tips or industrial sites. Check springs and wells for pollution. Field ponds are usually contaminated and may be stagnant.
Sand and Clay Filters :
These consist of 5-gallon (22.5 litre) plastic drums with the top removed and the bottom perforated ten times near its centre. The drum should be stood on a strong support so that a bowl or bucket can be taken from beneath it. Two inches (5 cm) of clean gravel is then put into the base of the drum, followed by a layer of towelling. Dig down below the topsoil into clay subsoil, sift the clay and remove any small stones, before placing about 10 inches (250 mm) of half and half clay/sand mix into the drum. Finish with another layer of towelling. This filter will remove contamination from dissolved oils, some bacteria and even some dissolved radioactive substances.
If a similar filter is made using washed sand, this will make a good clarifier to remove suspended sediment before the water is put through the clay filter.
These simple filters are good for about 500 litres, after which they should be emptied, cleaned and re-made.
Water Purification and Sterilisation
The following processes of purification can be used :-
- Settling / Sedimentation : Leave cloudy water to settle for as long as possible, decanting the purer water near the surface into containers for further purification. Use a large cistern to settle raw water.
- Flocculation : This is the settlement of fine particles by giving them something to latch onto, so that they sink together. The safest to use are clean clay from a sifted and pulverised dry subsoil, or to use building lime. Stir them in with a stick and leave the mud to settle.
- Filtration : Usually through a strainer, then through a sandy clay filter. Very effective - large sand filter beds accumulate a 'floc' of bacteria that consume all organic material and produce the best drinking water. Small domestic clay filters are less efficient but can work well in their way. For those who can afford it, aquarium filter wool and activated charcoal makes an excellent filter.
- Wick Filtration : This simple but remarkably effective system uses a strip of cloth towelling in a bucket of cloudy water to act as a syphon to a bucket set rather lower than the first. As the towel can only transport the liquid water by capillary action, sediment and some gross bacteria are left behind in the top bucket, relatively clean water dripping into the lower one. The only snag is that this is a fairly slow system and (unlike a clay filter) harmful chemicals dissolved in the water are not removed. The towelling will also eventually become clogged and will need to be boiled up before re-use. However, it is suggested that wick filtration be used after clay filtration to clarify the water further before sterilisation.
In addition, there are seven methods of sterilising water once purified by other means as far as can be managed :-
- Boiling for 20 Minutes : This requires a lot of fuel but it is highly effective. If carried out with a still to catch and condense the steam, distilled water can be produced at the same time, reducing losses and producing a useful by-product.
- Distillation : This requires a source of heat to boil the impure water in a closed container, steam given off being piped into a cooled container, or gathered in a clean cloth that is then wrung out into a container. Simpler expedients heated by the sun can evaporate water at lower temperatures and collect the condensed water.
- Chlorination : Add a teaspoon (5 ml) of Milton solution to every 5 gallons.
- Iodisation : Two drops of iodine solution per litre.
- Excess lime sterilisation : Hydrated lime added to water in fairly large amounts and then stirred up will act as a powerful bactericide; the disadvantage is that filtration or wick filtering will be needed to remove the lime and the water will be 'hard' enough to leave deposits if boiled in a kettle.
- Make up a 2% solution of alcohol with the water by diluting wine, beer or spirits in appropriate proportions.
- Exotic solutions include ultra-violet (UV) lamps, ozone generators, reverse-osmosis membrane filters and ion-exchange units - all effective, generally power-hungry and expensive.
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