Water is the single most critical input for food production. Understanding the water requirements of your garden, greenhouse, and any small livestock is essential for sizing your collection and storage systems correctly.
Plants lose water through transpiration, and soil loses it through evaporation. Combined, this is evapotranspiration (ET), measured in mm/day.
Typical ET values for temperate France:
| Month | ET₀ (mm/day) | Monthly Total (mm) |
|---|---|---|
| January | 0.5 | 15 |
| February | 0.8 | 22 |
| March | 1.5 | 47 |
| April | 2.5 | 75 |
| May | 3.5 | 109 |
| June | 4.5 | 135 |
| July | 5.0 | 155 |
| August | 4.5 | 140 |
| September | 3.0 | 90 |
| October | 1.5 | 47 |
| November | 0.8 | 24 |
| December | 0.5 | 16 |
| Annual | — | 875 |
Note: 1 mm of ET = 1 L/m² of water needed. Rainfall covers a portion of this; irrigation makes up the deficit.
For our reference location (800 mm rainfall/year), the irrigation season is primarily May–September. During these months:
For a 200 m² vegetable garden: \(\text{Irrigation need} = 200 \times 330 = 66{,}000 \text{ L} = 66 \text{ m³/season}\)
With efficient drip irrigation (30–50% water savings vs. sprinkler): \(\text{Efficient irrigation} = 200 \times 330 \times 0.6 = 39{,}600 \text{ L} ≈ 40 \text{ m³/season}\)
Different crops have very different water demands:
| Crop | Water Need (L/m²/season) | Yield (kg/m²) | L per kg produced |
|---|---|---|---|
| Tomatoes | 400–600 | 5–10 | 60–120 |
| Zucchini | 300–500 | 3–6 | 80–150 |
| Lettuce/salad | 200–300 | 2–4 | 75–150 |
| Beans | 250–400 | 1–3 | 130–300 |
| Potatoes | 300–500 | 3–5 | 80–150 |
| Onions/garlic | 200–300 | 2–4 | 75–100 |
| Carrots | 300–400 | 3–5 | 80–120 |
| Peas | 200–350 | 1–2 | 175–300 |
| Fruit trees (mature) | 500–800 per tree | 20–80 per tree | 10–30 |
| Strawberries | 300–500 | 1–2 | 250–400 |
Mulching reduces water needs by 30–50% by limiting soil evaporation. This is the single most cost-effective water conservation technique:
| Mulch Type | Water Savings | Additional Benefits |
|---|---|---|
| Straw (10–15 cm) | 40–50% | Decomposes into organic matter |
| Wood chips (5–10 cm) | 35–45% | Long-lasting, weed suppression |
| Compost layer (3–5 cm) | 25–35% | Feeds soil, improves structure |
| Living mulch (ground cover) | 20–30% | Biodiversity, nitrogen fixation |
| Plastic mulch | 50–60% | No soil benefit, not sustainable |
With mulching + drip irrigation, the 200 m² garden’s water need drops to: \(40 \times 0.55 = 22 \text{ m³/season}\)
The gold standard for autonomous gardens:
If your water tank is elevated (2–3 m above garden level), you can run drip irrigation without a pump:
\[P = \rho \times g \times h = 1000 \times 9.81 \times 3 = 29{,}430 \text{ Pa} ≈ 0.3 \text{ bar}\]At 0.3 bar, low-pressure drip emitters deliver ~1–2 L/h — sufficient for most gardens. Use a dedicated 1,000–3,000 L elevated tank for garden irrigation.
Cost for gravity-fed setup:
Smart irrigation controllers save 20–40% additional water:
| Feature | Benefit | Cost |
|---|---|---|
| Soil moisture sensors | Water only when needed | €20–50 per sensor |
| Weather-based scheduling | Skip irrigation before rain | €50–150 (controller) |
| Zone control | Different schedules for different crops | €100–200 |
| Flow monitoring | Detect leaks, track consumption | €50–100 |
A complete automated drip system with sensors: €500–1,200
A greenhouse (20–30 m² is typical for a family) has unique water considerations:
| Parameter | Value |
|---|---|
| Size | 25 m² |
| Growing season | Year-round (heated) or March–November (unheated) |
| ET inside greenhouse | 2–6 mm/day (higher than outdoor — enclosed heat) |
| Annual irrigation need | ~500–800 mm = 12–20 m³ |
| Roof collection potential | 25 m² × 800 mm × 0.9 = 18 m³ |
A greenhouse can be water-neutral — its roof collects enough rain to meet its own irrigation needs, with surplus in winter months.
In cold weather, greenhouse air condenses water on interior surfaces. This can be collected:
Aquaponics combines fish farming (aquaculture) with soilless plant growing (hydroponics) in a closed water loop.
| System | Water Use (L per kg of produce) |
|---|---|
| Traditional irrigated garden | 100–300 |
| Drip-irrigated garden | 60–150 |
| Aquaponics | 10–30 |
Aquaponics uses 90% less water than conventional gardening because water recirculates continuously. The only losses are evaporation and plant transpiration.
| Component | Specification | Cost |
|---|---|---|
| Fish tank | 1,000 L IBC tote | €100–200 |
| Grow beds | 3–4 × 200 L media beds | €200–400 |
| Pump | 40–60W submersible | €50–100 |
| Air pump | 10–20W for aeration | €30–50 |
| Plumbing | PVC pipes, fittings, bell siphons | €100–200 |
| Growing media | Expanded clay (LECA), 500 L | €100–200 |
| Fish stock | 50–100 tilapia or trout fingerlings | €50–150 |
| Total | — | €630–1,300 |
Production potential:
For a 200 m² garden with drip irrigation and mulching (22 m³/season):
Peak demand occurs in July: ~155 mm ET, ~40 mm rainfall = 115 mm deficit \(\text{July demand} = 200 \times 115 \times 0.6 \times 0.55 = 7{,}590 \text{ L}\)
Between rain events, you need buffer storage. A 5,000–10,000 L tank dedicated to the garden covers 2–4 weeks of peak summer demand.
Rainwater is excellent for gardens:
No treatment is needed for garden irrigation.
If your autonomous home includes small animals:
| Animal | Daily Water (L) | Annual (m³) | Notes |
|---|---|---|---|
| Chickens (6 hens) | 3–5 | 1.1–1.8 | More in summer |
| Rabbits (4) | 1–2 | 0.4–0.7 | Clean water essential |
| Goats (2) | 10–20 | 3.6–7.3 | Plus pasture irrigation |
| Ducks (4) | 4–8 | 1.5–2.9 | Need pond/bathing water |
| Bees (2 hives) | 0.5–1 | 0.2–0.4 | Nearby water source |
Total for chickens + rabbits (typical small autonomous setup): ~2–3 m³/year — negligible compared to garden needs.
| Category | Annual m³ | Source |
|---|---|---|
| Household (indoor) | 120–160 | Rainwater + well (filtered) |
| Garden (200 m², efficient) | 22–40 | Rainwater (unfiltered) |
| Greenhouse (25 m²) | 12–20 | Greenhouse roof collection |
| Chickens + rabbits | 2–3 | Any clean water source |
| Total | 156–223 m³ | — |
| Rainwater collection (160 m²) | 109 m³ | — |
| Greywater recycling | 60–80 m³ | — |
| Total supply | 169–189 m³ | — |
Verdict: With a well-designed system (large collection area + greywater recycling), water autonomy is achievable in most temperate climates. A well or borehole provides margin for dry years.
📊 Quick Reference — Garden Water System:
| Item | Cost |
|---|---|
| Drip irrigation (200 m²) | €300–600 |
| Garden water tank (5,000 L) | €500–1,000 |
| Automated controller + sensors | €200–400 |
| Mulching materials (annual) | €50–150 |
| Aquaponics system (optional) | €600–1,300 |
| Total garden water system | €1,000–2,500 |
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