A field sanitation program does not start with a supplier catalog. It starts with a population count and a ratio, because the number of latrine units a camp needs is not a matter of judgment — it is arithmetic laid down by the humanitarian sector’s own minimum standards. Getting that arithmetic wrong in either direction has consequences: too few units and queuing pushes people toward open defecation; too many and scarce procurement budget is diverted from water treatment or cold chain. This piece works through the actual sizing logic behind a field sanitation supplies order, using the reference ratios humanitarian WASH teams are expected to apply.
The core ratio: one latrine per twenty people
The starting figure most WASH coordinators plan against is the Sphere Handbook’s minimum standard of one toilet for every 20 people. That single number is the multiplier that turns a camp’s population figure into a procurement quantity: a settlement of 4,000 people implies a minimum of 200 latrine units, before accounting for maintenance downtime, decommissioning of full pits, or phased population growth. Programs that only budget to this bare minimum tend to discover the gap quickly, because the ratio assumes every unit is functional on any given day — a pit awaiting desludging or a superstructure needing repair does not count toward the total.
This is where the sizing exercise becomes a procurement exercise rather than a planning-document exercise. A desk ordering slabs, superstructure kits, or prefabricated cubicles has to build in a buffer above the raw 1:20 figure specifically to cover units that will be offline for cleaning, repair, or fecal sludge removal at any given time, or the camp will fall below the standard the moment the first unit fails.
Distance rules shape where units go, not just how many
Population count sets the quantity; distance rules set the layout, and layout errors are expensive to fix after installation. Two distance thresholds matter most for a field sanitation program:
- Maximum distance to a toilet: no shelter should be more than 50 meters from a toilet facility. This is a safety standard as much as a convenience one — women and children walking further than that after dark are exposed to real protection risks, and camp layouts that ignore it tend to see latrines built close to entrances instead of spread through the site.
- Minimum distance from groundwater: toilets should sit at least 30 meters from any groundwater source, and the bottom of a pit should remain at least 1.5 meters above the water table. Skipping this rule doesn’t just violate a guideline — it risks contaminating the same water supply the camp depends on, turning a sanitation gap into a waterborne-disease outbreak.
Neither rule is optional in the way "recommended" language sometimes implies elsewhere in program design. A camp map that satisfies the 1:20 ratio on paper but clusters units near a borehole, or strings them along a single row more than 50 meters from half the shelters, has not actually met the standard.
Sizing table: what the ratios mean in practice
| Standard | Minimum requirement | Procurement implication |
|---|---|---|
| Toilets per population | 1 per 20 people | Sets the base unit count; add a maintenance/downtime buffer above it |
| Distance from shelter to toilet | 50 meters maximum | Drives unit distribution across the site, not just total quantity |
| Distance from toilet to groundwater source | 30 meters minimum | Constrains where units can be sited relative to wells and boreholes |
| Pit bottom above water table | 1.5 meters minimum | Determines pit depth and whether raised or lined designs are needed |
| Gender separation | Male and female facilities separated | Effectively doubles the site-planning constraint — two distributed networks, not one |
| Handwashing access | Soap or an ash-based alternative at communal toilets | Every latrine order needs a paired handwashing-station line item |
Gender separation doubles the planning problem, not the unit count
The 1:20 figure is a population-wide ratio, but Sphere’s expectation that male and female facilities be kept separate means a program is effectively running two distributed networks across the same site, each needing its own compliant spacing and each needing to preserve privacy and cultural appropriateness in siting and design. A camp that treats this as a footnote — adding a signage change to a single latrine block instead of planning two genuinely separate, appropriately located sets of facilities — tends to under-serve women and girls specifically, since shared or poorly sited facilities are exactly what drives avoidance and the health and protection risks that come with it.
The handwashing line item that gets forgotten
A latrine order that stops at the toilet unit itself is incomplete. The same standard that sets the 1:20 ratio also expects users to have a way to wash their hands — soap where it’s available, an ash-based alternative where it isn’t — specifically at the point of leaving a communal toilet. In practice this means a field sanitation supplies procurement list should pair every batch of latrine units with a matching count of handwashing stations, sited at the exit rather than somewhere else in the camp, and a resupply plan for soap or its substitute. Treating handwashing as a separate, later purchase rather than a paired line item is one of the more common ways a program technically meets its latrine ratio while still leaving a hygiene gap open.
Conclusion
None of this is complicated math, but it is unforgiving math: the 1:20 ratio, the 50-meter and 30-meter distance rules, the 1.5-meter pit clearance, gender-separated networks, and paired handwashing access are not independent design choices a field team can trade off against each other. They are a single interlocking specification, and a procurement plan for field sanitation supplies has to size against all of them together — population count, maintenance buffer, site layout, and hygiene pairing — not just the headline ratio. Programs that plan to the full standard from the outset spend less time retrofitting a camp’s sanitation layout after the fact, which is usually the more expensive path.