Gravity-Fed Water & Plumbing Systems
Gravity is free, reliable, and requires no maintenance. A gravity-fed water system uses the natural elevation difference between a water source and your settlement to create pressure and flow without pumps, electricity, or moving parts. Roman aqueducts used this principle to deliver water across hundreds of kilometers. Your system will be simpler but follows exactly the same physics.
Fundamentals: Head Pressure
Every meter of elevation difference between your water source and your tap creates approximately 0.1 bar (1.4 psi) of pressure. This is called “head.”
- 5m head = 0.5 bar — enough for a trickle from a tap
- 10m head = 1.0 bar — adequate for a simple kitchen tap and garden hose
- 20m head = 2.0 bar — good working pressure, comparable to low-pressure municipal water
- 30m+ head = 3.0+ bar — excellent pressure, enables multiple simultaneous taps
To measure head: use a long hose filled with water, held at the source and at the delivery point. The water level difference in the hose equals the available head. Alternatively, use an altimeter, topographic map, or the smartphone method (if devices still function).
Minimum practical head for indoor plumbing: 8-10 meters. Below this, flow rate is too slow for comfortable use. If your natural source doesn’t provide enough head, you need an elevated storage tank.
Water Source Collection
Spring Box
A spring box captures water emerging from the ground and directs it into your pipe system.
Construction:
- Excavate carefully around the spring emergence point. Don’t dig into the aquifer—you risk redirecting the flow
- Build a small box (stone, concrete block, or earthbag) around the spring, open at the bottom where water enters
- Install an overflow pipe near the top (larger diameter than your supply pipe)
- Install your supply pipe 5-10cm below the overflow level
- Install a cleanout drain at the bottom (plugged valve)
- Cover with a tight-fitting lid to prevent contamination
- Backfill around the box with gravel for drainage, then earth
The spring box creates a small reservoir that provides consistent flow even when spring output fluctuates.
Stream Intake
For stream-fed systems, build an intake that captures clean water while excluding debris:
- Build a small dam or weir across the stream (rocks, logs, sandbags)
- Install a screened intake pipe upstream of the dam, positioned above the stream bottom (to avoid sucking in sediment)
- Use a settling basin (a small pond or tank) between the intake and your main pipe to let sediment drop out
- Include an overflow to handle high water without pressurizing or damaging your system
Pipe Materials
Salvaged Modern Pipe (Best Option)
PVC, polyethylene (PE), and copper pipe from pre-collapse construction is the most practical choice. It’s durable, leak-resistant, and comes with fittings designed for the purpose.
Where to salvage:
- Plumbing supply stores and warehouses
- Abandoned construction sites
- Under streets (water mains) and in building walls
- Agricultural irrigation systems (large diameter PE pipe)
- Garden hose is PVC pipe—it works for small systems
Bamboo Pipe
Bamboo makes excellent pipe where available. Select straight culms (sections) of 5-10cm diameter.
Method:
- Knock out the internal nodes (the solid dividers inside the bamboo) using a long rod or heated iron rod
- Joint sections by inserting a smaller diameter bamboo into a larger one, or by wrapping joints with cordage and sealing with pine pitch, beeswax, or clay
- Support every 1-2 meters to prevent sagging
Bamboo pipe lasts 2-5 years before needing replacement. It’s fast to make and easy to repair.
Wooden Pipe (Bored Log)
Historical water systems used bored logs extensively. Elm wood was preferred (it resists rot when wet).
Method:
- Select straight logs 10-15cm diameter
- Bore a hole through the center using a long auger (a large drill bit with a T-handle)
- Joint logs by tapering one end and socketing into the next
- Seal joints with tallow, pitch, or clay
Bored log pipes last 15-30 years in wet service. They’re labor-intensive but very durable.
Clay Pipe
Fired clay pipe is extremely durable (Roman clay pipes still function 2,000 years later) but fragile and heavy.
Method:
- Roll clay around a wooden form to create pipe sections 30-60cm long
- Create bell-and-spigot joints (one end wider than the other)
- Fire in a kiln to vitrify the clay
- Join sections with clay mortar or lime mortar
Best for permanent buried installations where the pipe won’t be disturbed.
Storage Tanks
Even a reliable spring fluctuates. A storage tank ensures consistent supply during low-flow periods and provides buffer for peak demand.
Sizing
Minimum storage: 3 days of supply for your household/settlement.
Water consumption per person per day:
- Drinking and cooking: 5-10 liters
- Washing and hygiene: 15-30 liters
- Laundry: 10-20 liters
- Garden irrigation: highly variable (50-200+ liters per 100 m²)
A family of 4 should have at minimum 400-600 liters of storage. A community of 30 should have 5,000-10,000 liters minimum.
Elevated Tank Placement
The tank must be higher than your highest tap. Every meter of elevation between tank bottom and tap equals 0.1 bar of pressure.
Common approaches:
- Hillside tank — use natural terrain. Pipe from source to a tank on the hillside, then pipe from tank to buildings below
- Tower tank — build a platform or tower to elevate a tank above the settlement. A 3m tower with a 2m-tall tank puts taps 3-5m below the tank bottom
- Rooftop tank — place a tank on a strong building roof. Simple but requires a strong roof structure (1,000 liters = 1,000 kg)
Ferrocement Tank
Ferrocement is a thin shell of cement plaster over wire mesh. It creates strong, watertight tanks with minimal cement.
Construction:
- Build a cylindrical form from wire mesh (chicken wire works) supported by rebar hoops
- Plaster both sides with cement-sand mortar (1:3 ratio), total thickness 3-5cm
- Cure slowly (keep moist for 7+ days)
- Coat interior with cement slurry for waterproofing
A 2m diameter × 2m tall ferrocement tank holds approximately 6,000 liters and uses only a few bags of cement.
Distribution
Simple Taps
The simplest tap is a plug valve: a wooden plug pushed into a pipe opening. Pull it out to flow, push it in to stop. Crude but effective.
Better: a gate valve salvaged from plumbing supply, or a wooden barrel spigot inserted into the pipe. You can carve functional taps from hardwood with a drilled bore and a rotating plug.
Indoor Plumbing Layout
For indoor plumbing, keep it simple:
- Run a single supply line into the building
- Branch to kitchen sink, wash basin, and any other fixtures
- Use the highest practical pipe routing to maintain pressure at all fixtures
- Install a shutoff valve at the building entry point
- Slope all drain pipes at minimum 2% grade (2cm drop per meter) toward greywater-recycling system or dry well
Hot Water
A thermosiphon system provides hot water using only fire and gravity:
- Mount a dark-colored metal tank (or coil of black pipe) above your wood stove or fireplace
- Connect the bottom of the heating vessel to the bottom of a storage tank (positioned higher)
- Connect the top of the heating vessel to the top of the storage tank
- As water heats in the vessel, it rises and flows to the storage tank. Cool water sinks from the storage tank to the heating vessel. This creates continuous circulation with no pump
The storage tank must be above the heating point for thermosiphon to work. Even a 30cm height difference is sufficient.
Maintenance
- Flush the system seasonally by opening all taps and drain valves
- Check the spring box or intake monthly for debris, animal intrusion, or contamination
- Inspect joints during dry weather—leaks are easier to spot when the ground isn’t wet
- Drain exposed pipes before freezing weather or bury them below frost depth
- Clean the storage tank annually—drain, scrub, and refill