Choose a settlement site by its water first: you need a source that keeps flowing through the driest season, clean enough to treat, and within reach of where people will live. Humanitarian survival standards (the Sphere Handbook) set at least 15 litres per person per day and a water point no more than 500 metres from any household, so a family of five needs about 75 litres a day.
Hydrology applied to siting: where water comes from, how much of it there is in the worst season, and how it threatens a site as well as serving it.
The Driest Month Decides Whether a Site Works
A site is judged by its worst week of water, not its best. A stream that roars in spring and shrinks to a trickle by late summer gives a false impression to anyone who visits once, in the wet season. Everything on this page is a way of finding out the minimum, not the typical.
The carrier article puts the ideal site above a reliable source by 5-30 meters of elevation: close enough to reach, high enough to stay out of floods. Note what that trades away. A site above its water must haul the water up, or lift it with a ram pump. A site below a hillside spring can run a gravity pipe to the houses (see Gravity-Fed Water & Plumbing Systems), but then sits lower than its source. Neither is wrong; know which one you are choosing.
Four Things to Establish for Every Source
- Reliability — does it run in the driest season? Ask locals, look for water-loving trees such as willow and alder, and revisit at the end of the dry season if you can.
- Quantity — is there enough at the minimum? See River & Stream Assessment and Spring Identification.
- Quality — can it be made safe? See Water Quality Indicators and Water Purification.
- Safety of the site — can the same water drown you? See Watershed Position & Flood Risk.
What Carrying Water Really Costs
Take the survival standard above and a household of five.
- Water: 5 people x 15 L = 75 L per day. One litre of water weighs about one kilogram, so that is about 75 kg a day.
- Containers: with 20 L containers, 75 / 20 = 3.75, so four trips.
- Distance: at the 500 m limit each trip is 500 m out and 500 m back, 1 km. Four trips is 4 km a day, about 48 minutes at a walking pace of 5 km/h.
That is a household spending most of an hour every day moving water, at the maximum acceptable distance and the minimum acceptable volume. A source at 100 m cuts the walk to about 10 minutes; piped water removes it. This is the labor the carrier means by “hauling water uphill for every day it exists”.
Common Mistakes
- Judging by one visit — a single spring visit sees the wet-season flow. Test the end of the dry season, or ask people who have lived there through one.
- Treating “near water” as “next to water” — floods, insects and dampness all rise near the channel. The carrier rule is at least 50 meters from the main channel and at least 3 meters above the highest visible flood evidence.
- Assuming clear means safe — see the danger below.
Safety
Clear water is not safe water
Pathogens, nitrate and dissolved metals are invisible. Treat every source before drinking, and keep latrines, livestock and washing downstream and downslope of the intake. Boiling kills pathogens but does not remove nitrate or metals.
What’s Next
- Learn next: Surface Water Sources — rivers, streams and springs compared
- Combine with: Groundwater & Well Potential — when no surface source exists