Safe water and drinks at home

Household treatment works by four different physical or chemical mechanisms, and knowing them explains each method’s limits. Boiling uses heat: above about 70°C the proteins and enzymes of bacterial and protozoan cells denature, and viruses are inactivated by heat damage to their structure and genetic material, so a true rolling boil is far more than any of them tolerate. Chlorination is oxidation: sodium hypochlorite hydrolyses in water to hypochlorous acid (HOCl), the small uncharged molecule that crosses the cell wall and attacks enzymes and nucleic acids. Its power is summarised by the CT value, the concentration of free chlorine multiplied by the contact time, which is why halving the dose demands roughly doubling the wait. Chlorine is consumed by dirt, so turbidity above about 5 nephelometric turbidity units must be reduced first, and Cryptosporidium oocysts are essentially resistant because their thick wall blocks HOCl. Ultraviolet light, used by SODIS and by UV lamps, is absorbed by nucleic acids and joins adjacent thymine bases into dimers that stop replication, so the germ is inactivated rather than removed; UV therefore needs clear water and an adequate dose, and SODIS depends on at least six hours of strong sun. Filtration is mechanical: pores of about 0.2 micrometre sieve out cysts of 4 to 15 micrometres and most bacteria of 0.5 to 2 micrometres, while viruses of 20 to 250 nanometres pass straight through. Silver-impregnated ceramic adds a slow bacteriostatic effect, not a virus barrier. Results are quoted as log reductions — a 2-log reduction removes 99% and a 4-log reduction 99.99% — and regulators expect several logs of virus, bacteria and protozoa, which is why a single weak method is normally combined with a second barrier rather than trusted alone.

Public health treats drinking water as a chain that runs from the catchment to the cup, and household treatment is only one link in it. The steps are the catchment and the source (a protected spring, borehole, well or piped network); abstraction, where water is drawn; collection with clean containers and no dipping; transport and household storage of untreated water; treatment; safe storage; and serving. A water safety plan starts from the same idea: identify the hazards at every step, then control them where they can be controlled. In the field the weakest link is found with two simple tools. A sanitary inspection walks the chain and scores visible risks — an unprotected well head, a rope lying on the ground, a latrine within ten metres, an open storage bucket, animals near the container. A microbiological test then confirms contamination: water is checked for Escherichia coli or thermotolerant coliforms, which indicate faecal pollution, and the reference standard for a treated supply is no detectable colony-forming units per 100 millilitres. Where no laboratory is available, a hydrogen sulphide vial test gives a cheap field signal. Measuring free chlorine residual at the point of use closes the loop, because a treated supply should still hold roughly 0.2 to 0.5 milligrams per litre. The important implication is that testing the source alone can mislead: a protected source with an open bucket at home passes the source test and still delivers contaminated water. This is why global monitoring now counts safely managed drinking water — accessible on the premises, available when needed and free of contamination — instead of counting improved sources only.

Behaviour change is a clinical skill, and household water treatment asks for a sequence rather than a slogan. First, assess: the nurse maps the household chain and listens for the family’s own explanation of illness, cost and convenience. Second, tailor: advice that ignores affordability, fuel supply, the caregiver’s literacy or the distance to the source will not be followed. A household that cannot buy charcoal may accept a chlorine tablet or a SODIS bottle; a household with unlimited firewood may prefer boiling. Third, demonstrate with the family’s own equipment, because adults learn a technique by doing it and by watching the water, the tablet and the bottle. Fourth, use teach-back: the caregiver explains and performs the routine in her own words, which exposes misunderstandings that a question such as “Do you understand?” never reveals. Fifth, reinforce at every contact — immunisation visits, growth monitoring, illness reviews — because a new habit competes with an old one and needs repetition and social support. Two further principles matter. Prioritise the people who prepare drinks, usually women and older children, and include men when they control household spending. And avoid blame: when a family has no safe source within reach, the nurse documents the barrier and refers it to the community health service rather than turning a structural problem into a personal failure. Documentation completes the cycle, because the next nurse needs to know which method was agreed and whether it worked.