What this planner estimates
This calculator projects how much liquid water a passive dew-harvesting mesh can collect over a chosen number of nights. It is designed for quick feasibility checks and early-stage sizing: you enter the mesh surface area, an average nightly dew deposition (often reported by weather stations or field measurements), an estimated collection efficiency, and the number of nights. The output includes a per-night table (useful for reports) and a total volume in liters.
Dew harvesting is not the same as rainfall harvesting. Dew forms when surfaces cool below the dew point and water vapor condenses. In many deserts, nights can be cold and clear even when days are hot, which can create conditions for condensation on radiatively cooled surfaces. Mesh collectors, foils, and panels are used because they can cool efficiently and provide a path for droplets to coalesce and drain into a gutter.
Inputs, units, and assumptions
- Mesh surface area (m²): the effective condensing area exposed to the sky. If you have multiple panels, sum their areas.
- Average nightly dew deposition (mm): the equivalent water depth that condenses per square meter per night. The calculator converts mm to meters internally.
- Collection efficiency (%): accounts for losses (droplets blown away, re-evaporation before drainage, imperfect gutters, splash, and wetting behavior). Use 0–100.
- Number of nights: how many nights you want to model. The tool assumes the same average deposition each night.
The model is intentionally simple: it treats dew deposition as uniform across the mesh and constant night-to-night. In reality, dew varies with humidity, cloud cover, wind, radiative cooling, dust, and site microclimate. For planning, you can rerun the calculator with low/typical/high dew values to create a range.
Formula used (and why liters appear)
Dew deposition is a depth. Multiplying depth by area gives a volume. Efficiency scales that volume down to what you actually collect. The nightly collected volume is:
Nightly volume (m³) = Area (m²) × Dew depth (m) × Efficiency (0–1)
The calculator then converts cubic meters to liters using 1 m³ = 1,000 L. A helpful rule of thumb falls out of this conversion: 1 mm of water over 1 m² equals 1 liter before efficiency losses. That means if you enter 0.3 mm and 20 m², the “raw” condensed amount is about 6 liters per night, and the efficiency reduces it to what you actually collect.
Worked example (step-by-step)
Imagine a small installation with 50 m² of mesh. Field notes suggest an average dew deposition of 0.2 mm per night. If the system captures about 60% of condensed water and you plan for 90 nights:
- Convert dew depth: 0.2 mm = 0.0002 m
- Nightly volume (m³): 50 × 0.0002 × 0.60 = 0.006 m³
- Nightly volume (L): 0.006 × 1,000 = 6 L/night
- Total over 90 nights: 6 × 90 = 540 L
That total is modest compared with rainfall harvesting in wet climates, but it can be meaningful for emergency storage, handwashing stations, seedling irrigation, livestock supplementation, or reducing the number of trips to a distant well.
How to choose realistic input values
If you have measurements, use them. If you do not, start with conservative assumptions and then test sensitivity. Dew deposition can be measured with a simple dew gauge or inferred from local studies. In some arid coastal deserts, fog and dew can be frequent; in inland deserts, dew may be sporadic and strongly seasonal. Because this planner uses an average nightly value, it is best used as a scenario tool: run it for a low value (dry spell), a typical value (seasonal average), and a high value (good nights) to understand the range.
Efficiency is often the hardest number to estimate. It bundles together many real-world effects: droplet formation, drainage speed, wind stripping, re-evaporation after sunrise, gutter design, and leaks. If you are planning a first installation, a practical starting range is 40–60%. Well-designed systems with good drainage and clean surfaces may perform higher, while dusty sites or poorly drained meshes may perform lower.
Design notes that affect yield (beyond the math)
The calculator’s output is only as good as the assumptions you feed it. The following field considerations can change real yield substantially, even when the “average dew deposition” seems similar between sites.
Placement and microclimate
Place collectors where they have a clear view of the night sky and good airflow. Ridges, open flats, and areas above low vegetation can work well. Avoid placing meshes right next to warm walls, roofs, or asphalt that radiate heat at night and reduce cooling. In some locations, a small change in elevation can move the collector into a cooler air layer, improving condensation.
Orientation, tilt, and drainage
A mesh that is too flat may hold droplets and encourage re-evaporation; a mesh that is too steep may shed droplets before they coalesce. Many installations use a moderate tilt so gravity helps water run into a gutter. Drainage paths should be smooth and continuous. If water pools on the mesh or in the gutter, it can evaporate quickly after sunrise, reducing the collected volume.
Surface condition and maintenance
Dust and salt can change wetting behavior and block pores. Insect debris and bird droppings can also reduce performance. Plan for routine cleaning, especially after wind events. Even a quick rinse can restore drainage. Maintenance is not just about yield: clean collection surfaces and clean gutters also reduce contamination risk.
Interpreting results for storage and use
The nightly table produced by the calculator repeats the same nightly yield because the model uses an average deposition. That repetition is useful for budgeting and for cumulative totals, but it should not be mistaken for a weather forecast. If you are sizing a tank, consider adding a buffer for variability: for example, size storage for a week or two of expected collection, and plan for periods with little or no dew.
For household planning, it can help to translate liters into daily tasks. A few liters per night might cover handwashing and cooking water for a small group, while larger installations can support nursery irrigation. If the water is intended for drinking, consider filtration and disinfection. Dew can be relatively low in dissolved salts compared with groundwater, but it can pick up dust, microbes, and residues from the collector surface.
Comparison of collection approaches (high-level)
Dew meshes are one option among several atmospheric-water strategies. This quick comparison is meant for context only; yields vary widely by climate. Passive systems trade higher variability for simplicity and low operating cost.
| Approach | Energy use | Typical yield | Notes |
|---|---|---|---|
| Passive mesh condenser | None | Low to medium | Simple, scalable, but sensitive to wind, dust, and night-sky exposure. |
| Radiative cooling panel | Low | Medium | Often uses engineered surfaces; may improve condensation under clear skies. |
| Active refrigeration / AWG | High | Medium to high | More predictable when powered, but higher cost and maintenance; needs electricity. |
Related tools
For understanding humidity conditions, consult our Absolute Humidity Calculator. If you are exploring other water sources, the Rainwater Harvesting Yield Calculator offers complementary estimates. Designers of hybrid systems may evaluate cooling performance with the Radiative Cooling Panel Power Calculator.
Limitations and responsible use
- This is an average-night model; it does not simulate weather variability, cloud cover, or seasonal changes.
- It does not account for storage losses, contamination, treatment requirements, or distribution losses.
- It assumes the entered area is the effective condensing area (not blocked by frames, shade cloth, or fouling).
- It assumes efficiency is constant; in practice, efficiency can change with cleanliness, temperature, and wind.
Use the CSV export to document scenarios (conservative/typical/optimistic) and to combine dew yield with other sources in a broader water plan. If you are making decisions that affect health or safety, validate assumptions with local measurements and consult relevant water-quality guidance.
Quick FAQ
Is “dew deposition” the same as rainfall?
No. Rainfall is precipitation from clouds; dew is condensation from water vapor near the ground when surfaces cool. Dew amounts are usually smaller than rain events, but dew can occur on many nights in some climates.
Why does the table show the same yield every night?
The calculator uses an average nightly dew deposition value, so the nightly yield is constant by design. To model variability, run multiple scenarios or split the season into segments with different average dew values.
What if my efficiency is unknown?
Start with a conservative estimate (for example 50%) and then test sensitivity by running 40%, 60%, and 80%. If you later measure real collection, update the efficiency to match observed performance.