Testing conditions in slums and informal settlements spans everything from satellite-based mapping to doorstep tuberculosis screening to water sampling that reveals contamination invisible to the naked eye. With roughly a billion people worldwide living in informal settlements, the stakes of getting these assessments right are enormous. Yet the picture that emerges from decades of field research is that conventional monitoring methods often miss what matters most, and the tests that do work tend to look very different from their counterparts in wealthier neighborhoods.
How Slums Get Identified in the First Place
Before any health or environmental test can happen, someone has to figure out where informal settlements actually are. Census data in many countries undercount slum populations, and municipal maps may not acknowledge settlements that governments consider illegal. Satellite imagery has become a workhorse for filling those gaps. Machine-learning models trained on very-high-resolution satellite images can now detect slum patches with moderate reliability, though accuracy drops when the images are lower resolution. One transfer-learning approach achieved a kappa value of 0.70 on very-high-resolution imagery but only 0.55 on medium-resolution images, suggesting that the finer details of rooftop materials and street patterns matter a great deal for automated detection.1Habitat International. Transfer learning approach to map urban slums using high and medium resolution satellite imagery
Community-led enumeration offers a ground-level alternative. Organizations affiliated with Slum Dwellers International have conducted household-by-household surveys in dozens of countries, collecting data on everything from income to tenure status to sanitation access. These enumerations serve a dual purpose: they generate data that governments can use for planning, and they help residents build collective identity and political leverage to negotiate for services.2Environment and Urbanization. Knowledge is power – informal communities assert their right to the city through SDI and community-led enumerations In Cuttack, India, participatory mapping with geographic information systems opened a sustained dialogue between informal settlement residents and city officials about upgrading priorities, and directly influenced how a central government fund was allocated.3Environment and Urbanization. Enabling participatory planning with GIS: a case study of settlement mapping in Cuttack, India
Water Quality Testing Reveals Daily Swings
Water testing in slum environments has challenged a basic assumption of global monitoring programs: that a household’s water quality is relatively stable from day to day. Fieldwork in Nairobi’s informal settlements found that bacterial contamination of household drinking water changed daily, and not a single household had water that was completely safe to drink every day. Households relied on multiple water sources and switched between them constantly depending on availability, cost, and which taps happened to be working. Residents’ own judgments about whether their water was safe bore little relationship to what the lab tests showed: E. coli levels were broadly similar in samples residents considered safe and those they considered unsafe.4PubMed. Daily changes in household water access and quality in urban slums undermine global safe water monitoring programmes
The problem compounds as water moves from the tap to the home. In slum households in Hawassa, Ethiopia, nearly half of household-stored water samples tested positive for total coliform bacteria, compared with about one in eight samples taken directly from the tap. Roughly a third of household samples contained fecal coliform, and about one in five fell into the World Health Organization’s “high-risk” category. The significant difference between tap-point and household contamination levels points to recontamination during transport and storage, a factor that standard infrastructure assessments miss entirely.5Applied Water Science. Physicochemical and microbial quality of drinking water in slum households of Hawassa City, Ethiopia
These findings have practical implications for how water programs are evaluated. A one-time snapshot showing that a community’s piped supply meets quality standards can be misleading if contamination fluctuates daily and if the real exposure point is the household storage container, not the pipe.
Tuberculosis Screening Uncovers Hidden Caseloads
Infectious disease testing in informal settlements routinely uncovers burden levels far above national averages. Tuberculosis is a clear example. In southeastern Nigeria, an active case-finding campaign screened over 16,000 people in urban slum communities and diagnosed TB in roughly 6% of those screened. On average, for every 16 people screened, one case was found. About two-thirds of cases were new smear-positive TB, the most infectious form, and nearly a quarter of cases also had HIV.6PubMed. Reaching the underserved: Active tuberculosis case finding in urban slums in southeastern Nigeria
Similar active screening in Kampala, Uganda, found that among chronic coughers in a slum community, roughly 18% had undiagnosed smear-positive TB.7PubMed Central. Active case finding of undetected tuberculosis among chronic coughers in a slum setting in Kampala, Uganda In Phnom Penh’s poor urban settlements, a 14-month campaign screened over 315,000 people and diagnosed 783 TB cases, with over 94% starting treatment and 81% completing it successfully. Rapid molecular testing (Xpert) added roughly 40-50% more diagnoses among people suspected of having drug-resistant or HIV-associated TB than microscopy alone would have caught.8PLOS ONE. Community-Based Active Tuberculosis Case Finding in Poor Urban Settlements of Phnom Penh, Cambodia: A Feasible and Effective Strategy
The consistent takeaway across these settings is that passive surveillance, waiting for sick people to show up at clinics, misses a large share of active TB in slum populations. Active door-to-door screening is resource-intensive but finds cases that would otherwise spread unchecked in crowded housing.
What Health Priorities Emerge When You Actually Ask
Beyond any single disease, researchers have tried to identify which health conditions should be prioritized for field-based screening in slum environments. A workshop-based study in Bangalore, India, synthesized clinical data and expert opinion to rank the most pressing health issues for urban slum screening. The top priorities that emerged were diabetes and hypertension among non-communicable diseases, dengue fever among infectious diseases, and malnutrition and anemia in the categories of child health and maternal health. Diarrhea was separately flagged as a top concern for children.9PubMed Central. Identification of priority health conditions for field-based screening in urban slums in Bangalore, India This list is striking because it mixes chronic conditions typically associated with wealthier populations (diabetes, hypertension) with infectious and nutritional diseases more commonly linked to poverty. Slum populations face both burdens simultaneously, which complicates screening program design.
Child Malnutrition and the Slum Penalty
Nutritional assessments in slum settings consistently show what researchers call an “urban slum penalty,” where children in informal settlements fare worse than both their rural and urban non-slum peers on key growth indicators. In urban Bangladesh, half of children under five living in slums were stunted and 43% were underweight, compared with 33% stunted and 26% underweight among children in non-slum urban areas. Severe malnutrition rates in slums were roughly double those in non-slum neighborhoods.10PubMed Central. Effects of individual, household and community characteristics on child nutritional status in the slums of urban Bangladesh
A broader review across Asia and the Pacific confirmed that nearly all indicators of infant and young child malnutrition were worse in urban slums, and that mothers living in slums had higher rates of underweight and iron deficiency anemia.11PubMed Central. What is missing in our understanding of urban slum environments and maternal, infant and young child nutrition from publicly available data in Asia and the Pacific? These findings challenge the common assumption that urban proximity to food markets and health facilities automatically translates into better nutrition. In slums, limited purchasing power and poor sanitation (which drives nutrient loss through repeated infections) can overwhelm the theoretical advantages of city living.
Mental Health Assessment in Informal Settlements
Mental health has historically received little screening attention in slum populations, but the evidence that has accumulated is alarming. A study of slum dwellers using standardized instruments found that roughly 73% of participants reported anxiety symptoms, 84% reported depression symptoms, and 69% reported stress-related problems. Being female, being married, having only one earner in the family, working as a day laborer, and being unable to afford children’s education were all associated with worse mental health outcomes.12PubMed Central. Assessing the mental health of slum dwellers: an ordinal logistic approach
A meta-analysis pooling data from 24 studies across low- and middle-income countries estimated that among young people in urban slums, about 31% met criteria for depression, 35% for anxiety disorders, 24% for post-traumatic stress disorder, and 23% for alcohol use disorders.13PubMed Central. Prevalence of mental disorders among young people living in urban slums of low- and middle- income countries: A systematic review and Meta-analysis These rates are several times higher than general population estimates in the same countries. The practical barrier is that mental health screening in slum communities remains rare, and even when conditions are identified, referral pathways to affordable treatment are often nonexistent.
Heat Stress and Indoor Environmental Monitoring
Environmental testing inside slum dwellings has revealed indoor conditions that most building codes would consider unacceptable. During a summer monitoring campaign in Kolkata, researchers placed sensors in 123 slum dwellings and 101 rural village houses about 75 kilometers away. Most dwellings in both settings exceeded safe heat-stress thresholds at some point during the day, but slum dwellings were hotter for longer. The coolest homes were rural structures made of mud walls and thatch roofs. The hottest were slum dwellings built with cement walls and corrugated tin or clay tile roofs. Crowding made things worse: the duration of dangerous indoor heat stress increased with the number of occupants and decreased with the number of rooms.14Building and Environment. Indoor heat conditions measured in urban slum and rural village housing in West Bengal, India
Low-cost interventions show promise. In Ahmedabad, testing of “cool roof” technologies in slum households found that approaches like thermocol insulation, solar-reflective white paint on the outer roof surface, and modular roofing panels effectively reduced indoor temperatures compared with untreated roofs.15PubMed Central. Combating Climate Change-induced Heat Stress: Assessing Cool Roofs and Its Impact on the Indoor Ambient Temperature of the Households in the Urban Slums of Ahmedabad Given that heat-related illness disproportionately affects the urban poor, these kinds of practical tests matter more than ever as cities warm.
Air quality monitoring tells a parallel story. In Nairobi’s Mukuru informal settlement, citizen-science volunteers carrying portable sensors recorded one-minute average fine particulate matter (PM2.5) concentrations ranging from around 6 to over 300 micrograms per cubic meter. Mean personal exposures for individual participants ranged from about 22 to 40 micrograms per cubic meter, with people whose work involved moving through the settlement (a door-to-door grocer, a street vendor) experiencing higher average exposure.16Applied Geography. Particulate matter pollution in an informal settlement in Nairobi: Using citizen science to make the invisible visible For context, the WHO’s annual-mean guideline for PM2.5 is 5 micrograms per cubic meter. Even the lowest individual mean recorded was several times that threshold.
Fire Risk Assessment
Fire testing in informal settlements has produced findings that challenge some intuitive assumptions about safety. Full-scale burn experiments using three dwellings clad in steel sheeting and three clad in timber showed that fire could spread from the first dwelling reaching flashover to the last dwelling reaching flashover in as little as four to nine minutes. Heat flux measurements, the first ever recorded for informal settlement dwellings, established that a separation distance of about 3.8 meters between structures was needed to prevent fire from jumping between them.17Fire Safety Journal. Experimental study of fire spread between multiple full scale informal settlement dwellings In many slum environments, actual dwelling-to-dwelling gaps are a fraction of that distance.
Settlement size also matters. A study of informal settlements of different scales in Costa Rica found that larger settlements tended to use more masonry and concrete, which naturally compartmentalized fire and slowed its spread. Smaller settlements relied more heavily on metal, gypsum, and wood sheeting, producing structures with a higher likelihood of fire spread due to lack of compartmentation.18Fire Safety Journal. A provisional fire risk characterization of informal settlements of different scales in San Jose, Costa Rica This is counterintuitive because large, dense settlements are usually assumed to be the highest fire risk, when in practice smaller settlements with flimsier materials can be more dangerous per dwelling.
Flood Vulnerability and Drainage Solutions
Informal settlements are frequently located on land that nobody else wants, which often means flood-prone terrain: riverbanks, low-lying areas, hillsides prone to erosion. Flood vulnerability assessments confirm that the combination of settlement location, building materials, and absent infrastructure creates compounding risk. Residents are pushed toward hazardous land precisely because they are excluded from safer areas by cost and legal barriers.19PubMed Central. Flood vulnerability in township informal settlements
Engineering interventions can work, though. In a settlement in Brazil built atop mountain headwaters, environmental assessment documented severe deforestation, disrupted water flows, permanent waterlogging, and intense erosion. A sustainable urban drainage system was constructed to redirect water flows to the main watercourse, and functional revegetation with native herbaceous and woody species was used to stabilize banks. One year after the intervention, the team documented reduced sediment runoff, restored channel capacity, and established riparian vegetation.20Environmental Development. Impact assessment and rehabilitation of an informal settlement using sustainable urban drainage systems as a nature-based solution in Brazil Nature-based drainage design is not typically tested in informal settlements, so this case stands out as proof that ecological engineering can be adapted for these contexts.
Evaluating Upgrading Policies
Perhaps the highest-stakes test of all is whether upgrading programs actually improve conditions. Research comparing two common policy approaches, in-situ upgrading (improving conditions where people already live) and population relocation (moving people elsewhere), found that both reduced the share of land used for housing within the original slum boundary. But only in-situ upgrading produced lasting improvements in housing quality and residents’ socioeconomic status. Upgrading also generated positive spillover effects in surrounding neighborhoods, increasing formal housing investment and reducing crime. And it was roughly one-third cheaper per household than relocation.21NBER. In-situ Upgrading or Population Relocation? Direct Impacts and Spatial Spillovers of Slum Renewal Policies
Land titling, often promoted as a foundational step toward slum improvement, has a more mixed track record. A broad review found that investment in land and housing, access to formal credit, and municipal revenues did not increase noticeably more under titling programs than under other tenure arrangements, and there was no significant evidence that titling reduced poverty.22Environment and Urbanization. The limits of land titling and home ownership In Dar es Salaam, the introduction of residential licenses created legal certainty but did not result in the financial sector accepting the licenses as full loan collateral, limiting the credit access that titling advocates had promised. The licenses did, however, enable formal property transactions within settlements, which is a meaningful if more modest achievement.23Land Use Policy. Impact of formalisation of property rights in informal settlements: Evidence from Dar es Salaam city
Economic Networks and Informal Labor Markets
Testing economic assumptions about slum populations also yields surprises. A survey of roughly 800 slum households in Delhi examined how residents found jobs and found that three types of social networks dominated: kinship ties, caste and ethnicity bonds, and formal channels like NGOs and employment exchanges. The nature of economic activities varied across different parts of the city, and the desire to live near a contact person or workplace made the urban labor market highly segmented. Residents did not simply flow to wherever jobs were; they clustered around network nodes in ways that created distinct economic geographies within the same city.24Review of Urban & Regional Development Studies. INFORMAL SECTOR, NETWORKS AND INTRA‐CITY VARIATIONS IN ACTIVITIES: FINDINGS FROM DELHI SLUMS
Electricity Access and the Gap Between Connection and Legality
Energy access surveys in informal settlements reveal a gap that headline electrification statistics hide. Data from Ghana’s informal settlements illustrate the issue well: while about 88% of informal settlement households had access to electricity, only about 46% acquired their connection legally and directly from the utility company. The remaining 54% connected through neighbors’ meters, a practice locally called “by-pass,” which is technically illegal.25Energy Research & Social Science. Electricity and informal settlements: Towards achieving SDG 7 in developing countries These shared, informal connections tend to be lower quality and more dangerous, with overloaded wiring contributing to the fire risks described earlier. From a policy standpoint, counting a settlement as “electrified” based on access alone paints a misleading picture of safety and service reliability.