Water quality and waterborne disease: practical protection for your household

How does safe water become dangerous?

Water that leaves a treatment plant clean does not necessarily arrive at your tap in the same condition. A study published in Water Research in 2013 compared microbial water quality in intermittent and continuous piped supply systems and found that intermittent supply carried substantially higher bacterial contamination. When water stops flowing and pressure in the pipes drops, contaminated water from surrounding soil or nearby sewage can be drawn in through any crack, joint or corroded section of pipework.

Household storage tanks create a second hazard. In a tank that is not cleaned regularly, algae, bacteria and a bacterial film known as biofilm accumulate gradually on the interior walls and contaminate water held there even if the incoming supply was clean. In hot climates, certain bacteria multiply rapidly in warm standing water. Any crack in a tank lid or its connecting pipes opens a route for contamination from air, insects or debris.

Areas where infrastructure has been disrupted by conflict or natural disaster face elevated risk. A review published in Frontiers in Public Health in 2023 documented the cholera outbreak in Syria as directly linked to the collapse of water supply and sanitation infrastructure, a pattern seen repeatedly across the region during crises. A case-control study of drinking water quality in Yemen, published in 2024, confirmed that households using unimproved water sources faced measurably higher risk of illness.

Boiling: the simplest and most reliable method

Boiling is the oldest and most reliably effective method for household water treatment. Temperatures above 70 degrees Celsius kill most pathogens, and a full rolling boil at sea level kills all common bacteria, viruses and parasites including Cryptosporidium and Giardia, both of which resist chlorine. At one minute of full boil, the water is safe. In higher altitude areas such as mountain regions, boil for three minutes because the boiling point decreases with altitude and pathogen kill takes longer.

Boiling does not remove chemical contamination or heavy metals such as lead and arsenic, and it does not improve taste caused by dissolved organic compounds. It is the right solution for microbial and parasitic contamination, which is the primary concern in most regional settings. After boiling, cool the water in a clean closed container and do not add any unboiled water to it, whether from a bottle or a tap.

The container you use for cooling and storing boiled water matters as much as the boiling itself. A metal or glass vessel with a secure lid prevents recontamination during the cooling and storage period. Avoid wide-mouthed plastic containers or any vessel that is not thoroughly clean. Contamination introduced during storage after boiling can negate the protection that the boiling provided.

Household chlorine: how to use it correctly

Chlorine is the most widely used method for treating larger quantities of water at very low cost. It is typically applied as sodium hypochlorite solution, which is the active ingredient in household bleach products available in most pharmacies and general stores. A landmark study published in Water Science and Technology in 2003 confirmed the effectiveness of household chlorine treatment in reducing bacterial contamination and diarrhoeal illness in settings comparable to those across the region.

The standard dose is generally two drops of a 5 to 6 percent sodium hypochlorite solution per litre of water. Stir well and wait at least 30 minutes before drinking. For turbid or visibly cloudy water, double the dose because organic matter in the water consumes chlorine and reduces its effectiveness. The treated water should have a faint smell of chlorine. If you cannot detect any chlorine odour after 30 minutes, add a little more and wait again.

Chlorine does not reliably kill Cryptosporidium or Giardia at safe household concentrations. If your area is experiencing an outbreak linked to either of these parasites, boiling is the required solution, not chlorination alone. Chlorine also loses effectiveness rapidly when exposed to sunlight and heat, so store your chlorine solution in a cool place away from direct light, and use it before its expiry date.

Household filters: which ones actually work?

Home water filters fall into two broad types: chemical filters that use chlorine or iodine to disinfect, and mechanical filters that physically block particles and microorganisms. A systematic review published in the Journal of Global Health in 2024 confirmed that fine-pore mechanical filters, specifically the hollow fibre type used in products such as the LifeStraw Family filter, produce a meaningful and measurable reduction in childhood diarrhoea when used consistently.

A hollow fibre filter with a pore size of 0.1 micrometres or smaller is the most effective mechanical option. At that scale it intercepts bacteria and parasites reliably. Activated carbon filters improve taste and odour and remove some chemical contaminants but do not disinfect water against bacteria. Combining a fine mechanical filter with chlorine treatment delivers broader protection than either method alone.

Every filter requires maintenance or it becomes a contamination source itself. Follow the manufacturer's instructions for replacing filter elements and cleaning the housing. A filter that has exceeded its rated operational life may release accumulated bacteria rather than retaining them. Note the installation date and change elements on schedule.

Keeping your water tank clean

Roof and ground-level household water storage tanks need to be cleaned at least every three months in hot climates, and every six months in cooler areas. Calcium carbonate deposits, algae and a bacterial layer known as biofilm accumulate gradually on the tank walls and contaminate the stored water even when the incoming supply is clean.

To clean the tank: empty it completely, then scrub the interior walls with a stiff brush or rough cloth without strongly scented chemical cleaners. Rinse thoroughly with water. Then prepare a chlorine solution using one litre of standard 5 percent bleach per thousand litres of tank capacity. Fill the tank with this solution and leave it for two hours before drinking. If the chlorine odour is strong after two hours, flush the tank once with clean water before use.

Check the tank lid. A damaged or poorly fitting lid allows insects, birds, dust and debris to enter, all of which are contamination routes. Never reach into the tank with a hand or dip a container directly into the water. Use a tap or small pump to draw water out. A hand introduced into the tank contaminates the water for everyone drawing from it.

Warning signs and when to see a doctor

Mild diarrhoea lasting one or two days in a healthy adult is usually managed at home with increased fluids and oral rehydration solution. But certain patterns require urgent medical assessment. Very profuse watery diarrhoea that makes it impossible to keep up with fluid intake, diarrhoea containing blood or mucus, fever above 39 degrees Celsius alongside diarrhoea, and any diarrhoea in a child under two years old all warrant medical evaluation.

Children under two are a specific priority because dehydration develops faster in young children and can become life-threatening within hours. The warning signs of severe dehydration are: no tears when crying, dry mouth and tongue, skin that does not spring back quickly when pinched, sunken eyes, very little or no urine for several hours, and lethargy or unusual drowsiness. Any of these in a young child is an emergency. Start oral rehydration solution immediately and get to a hospital.

An adult who develops a fever that rises gradually over several days, accompanied by headache and body aches, without another clear cause may have typhoid fever or hepatitis A, both of which spread through contaminated water and food and both of which need laboratory confirmation and proper medical treatment. These are not conditions to manage at home with available medicines.

Everyday prevention habits that genuinely reduce risk

Washing hands with soap before eating and after using the toilet is the single cheapest and most effective measure against waterborne and foodborne illness. The large Lancet meta-analysis published in 2022, reviewing interventions in low-income and middle-income settings, found that improvements in water quality combined with soap handwashing reduced childhood diarrhoea by up to 50 percent. The soap is not optional. Water alone removes far fewer pathogens than water with soap.

Do not drink from irrigation canals, rivers or ponds without treatment. These open water sources are common routes for Giardia, Cryptosporidium, Vibrio cholerae and typhoid bacteria in areas where sewage and water supplies are not fully separated. Vegetables irrigated with untreated water should be washed thoroughly in clean water or soaked briefly in chlorinated water before consumption.

When travelling to areas where you are unsure of water quality, factory-sealed bottles are the safest option. If those are not available, boiled water is the next best choice. Avoid ice in drinks at restaurants and street food stalls unless you are confident in its source, because ice made from untreated water carries the same risk as the water itself.

Hand hygiene at critical moments reduces disease transmission even when the water itself is not perfectly treated. The moments that matter most are before preparing or eating food, after using the toilet, after handling animals or soil, and after caring for someone who is ill. Keep a small bar of soap accessible at every hand-washing point in the house, because the habit only forms when the soap is already there.

When oral rehydration solution (ORS) is not commercially available, you can prepare a reliable home version by dissolving one level teaspoon of salt and six level teaspoons of sugar in one litre of cooled boiled water, with a squeeze of lemon juice if available. This replaces the salt and glucose lost through diarrhoea and prevents the dehydration that turns a manageable illness into a dangerous one. Carbonated drinks and concentrated fruit juices are not substitutes because their high sugar concentration can draw more fluid from the gut and worsen the situation.

Sources

• Wolf J, Hubbard S, Brauer M et al: Effectiveness of interventions to improve drinking water, sanitation, and handwashing with soap on risk of diarrhoeal disease in children in low-income and middle-income settings: a systematic review and meta-analysis, Lancet (London, England), 2022
• Kumpel E, Nelson KL: Comparing microbial water quality in an intermittent and continuous piped water supply, Water research, 2013
• Al-Hmani A, Ben Jamaa N, Kharroubi A et al: Case-control study of drinking water quality in Yemen, Eastern Mediterranean health journal, 2024
• Sobsey MD, Handzel T, Venczel L et al: Chlorination and safe storage of household drinking water in developing countries to reduce waterborne disease, Water science and technology, 2003
• Kerr M, Cardinale V, De Vito C et al: Lifestraw Family water filters in low- and middle-income countries: a systematic review and meta-analysis, Journal of global health, 2024
• Eneh SC, Admad S, Nazir A et al: Cholera outbreak in Syria amid humanitarian crisis: the epidemic threat, future health implications, and response strategy, Frontiers in public health, 2023
• World Health Organization: Guidelines for drinking-water quality, 4th edition incorporating the 1st and 2nd addenda