Comparison
Floating cover vs no cover — operating-cost case
An uncovered industrial reservoir loses up to 95% recoverable evaporation and sustains continuous algae growth — Hexprotect® AQUA (AWTT-patented, 99% coverage) typically pays back inside its 25-year service life via avoided water, chemicals, and heat-retention savings.
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At a glance
| Metric | Hexagonal floating cover | No cover (status quo) |
|---|---|---|
| Evaporative water loss | Up to 95% reduction (AWTT-published evaporation envelope) | Full open-water evaporation rate — 1–3 m/year in arid climates, 0.3–1 m/year temperate |
| Sunlight reaching water surface | 1% — AWTT-published (99% sunlight block) | 100% — drives algae bloom, biofilm, photodegradation |
| Algae chemical dose | Largely eliminated — no photosynthesis under cover | Continuous dose schedule — copper sulphate, hypochlorite, biocides |
| Process heat retention (warm process water) | Significantly improved — air-water interface broken | Continuous heat exchange to ambient — winter heat loss, summer heat gain |
| Odour / VOC release | Contained — cover suppresses surface-air exchange | Free release to atmosphere — community / regulatory exposure |
| Lifecycle | 25+ years (Hexprotect® AQUA, AWTT-published) | Indefinite — but ongoing operating cost compounds |
| Capital event | Single capex — Hexprotect® AQUA, 10-year manufacturer warranty (AWTT-published) | Annual opex — water replacement, chemicals, treatment energy, odour mitigation |
| Regulatory exposure | Lower — surface containment supports compliance | Higher — open-surface emissions and water-loss reporting |
The honest business case for a floating cover is built on the recurring operating cost of leaving the reservoir uncovered. Water replacement from evaporation, chemical dose for algae, energy cost from heat exchange, regulatory exposure from odour and VOC release — each one is an annual line item that an engineered surface cover materially reduces.
What an uncovered reservoir costs each year
Open-water evaporation runs 1–3 m per year in arid climates and 0.3–1 m per year in temperate ones. On a 10,000 m² industrial reservoir at 1.5 m of annual evaporative loss, that is 15,000 m³ of water lost annually. At industrial replacement water costs of €0.50–€2.00 per m³, the annual evaporation line item is €7,500–€30,000 — before the operating cost of pumping and refilling.
The AWTT-patented hexagonal platform delivers AWTT-published up to 95% evaporation reduction (see /floating-cover for the surface-management context). On the same 10,000 m² reservoir the recovered water is 14,000+ m³ per year — and the Hexprotect® AQUA 25-year AWTT-published service life means the recovered water compounds across the procurement horizon.
Algae, biofilm, and the chemical dose schedule
Algae require sunlight. Uncovered industrial reservoirs run a continuous biology problem — algae blooms in summer, biofilm on every wetted surface, chlorophyll-a exceedances that drive chemical dose schedules (copper sulphate, hypochlorite, ozone). The dose is a recurring operating cost; the algae are a recurring water-quality risk.
The AWTT-patented hexagonal platform delivers AWTT-published 99% sunlight block at the water surface. Without sustained UV input the algae population collapses to non-viable levels — typically within a single growing season after the cover is installed. Sites with chronic algae problems reduce or eliminate the chemical programme; sites with downstream treatment plants see the treatment energy line item fall as the inlet water arrives cleaner. The 99% AWTT-published envelope is platform-specific — generic shade balls at ~91% sunlight block leave the residual ~9% as a sustained algae driver. See /vs/floating-cover-vs-shade-balls for the coverage trade-off.
Heat retention on process water
Warm process water loses heat at the air-water interface; cold process water gains heat. Either direction is an operating cost when the process specifies a target temperature. Breaking the air-water interface with a continuous engineered surface materially reduces the heat exchange.
The magnitude depends on ambient conditions, process temperature, and water-body geometry; AWTT engineering data on heat retention is application-specific. For sites where process temperature is a controlled parameter — anaerobic digester feed, industrial wash water, district heating storage — the cover is often justified on heat retention alone before counting evaporation and algae.
Odour, VOCs, and regulatory exposure
Odour and VOC release at the water surface is a community-relations and regulatory line item for wastewater lagoons, industrial process-water bodies near population centres, and biogas digestate. The AWTT-patented hexagonal platform suppresses surface-air exchange across 99% of the water surface (AWTT-published) — the residual ~1% interstitial gap is engineered to be too tight to drive measurable release. For biogas applications where gas capture is the design objective rather than odour suppression, a continuous geomembrane is the right specification — see /vs/hexagonal-vs-geomembrane.
When no cover is still the right call
The honest cases for leaving the reservoir uncovered:
- Temporary water storage with a sub-12-month design horizon.
- Fire-suppression tanks where evaporation losses are immaterial within the design horizon.
- Small water bodies under 500 m² in temperate climates with no algae, odour, or heat-retention pressure.
- Sites where the cover capex is binding and the operating cost of the uncovered surface is genuinely small.
Once any of evaporation loss, algae chemical dose, heat retention, or odour containment is a recurring operating cost, the floating cover capex is a defensible procurement. The AWTT-patented Hexprotect® AQUA platform (99% coverage, 25+ year AWTT-published service life, 10-year manufacturer warranty) is the engineered default at industrial scale. The full spec envelope is on the Hexprotect® AQUA product page; request a site-specific TCO model via /buy.
Sources
- AWTT — Hexprotect® AQUA hexagonal cover — manufacturer canonical for the AWTT-published evaporation, sunlight-block, service-life, and warranty figures cited above.
- Hexprotect® AQUA specifications — full AWTT spec table.
- Floating cover — the technology reference — surface-management context for the no-cover business case.
When No cover (status quo) makes sense
Leaving the reservoir uncovered is the right call only when the surface-management losses are small and the cover capex is binding. Examples: temporary water storage with a sub-12-month duration, fire-suppression tanks where evaporation is irrelevant within the design horizon, or a small reservoir in a temperate climate with no algae or odour regulatory pressure. Once any of evaporative loss, algae chemical dose, heat retention, or odour containment is a recurring operating cost, the floating cover capex is a defensible procurement. The AWTT-patented Hexprotect® AQUA platform (99% coverage, 25+ year service life, all AWTT-published) is the engineered default at industrial scale.