Summer droughts are increasingly common across Portugal, particularly in the southern regions (Alentejo, Algarve) and inland areas where rainfall is scarce from June through September. Municipal water restrictions often follow with limited refilling, banned hosing of outdoor spaces, or fines for excessive water use, leaving pool owners concerned about whether maintaining their pools is responsible or even permissible during dry periods.
The good news: properly maintained pools use far less water than most people assume, often consuming less water annually than a lawn of equivalent size. The challenge: managing pools during drought requires different priorities than standard maintenance. This guide explains how to maintain clean, safe pool water while minimizing water consumption during Portugal’s summer drought conditions.
Key Takeaways
- Pool covers reduce evaporation by 70-95% and it’s the single most effective water conservation measure for pools.
- Evaporation is the primary water loss in pools (not swimmers or splashing). In Portugal’s hot, dry summers, uncovered pools can lose 6-10mm per day and 180-300 liters monthly for a typical 8m x 4m pool.
- Cartridge filters eliminate backwash water waste (3,000-6,000 liters annually) compared to sand or DE filters.
- Proper chemistry extends water life indefinitely. Balanced water doesn’t need draining and refilling.
- Leak detection is critical. A small leak wastes more water than normal evaporation.
- Natural pools are inherently drought-resilient. They require less makeup water due to shade from planted zones and no backwashing.
- Pools use less water than lawns of equivalent size when properly managed.
Understanding Pool Water Loss During Drought
Evaporation: The Primary Culprit
Evaporation accounts for 70-90% of water loss in well-maintained pools. Water molecules at the surface transition from liquid to vapor, particularly when:
- Air temperature is high (above 30°C, common in Portuguese summers)
- Water temperature is warm (heated pools or sun-warmed water)
- Humidity is low (dry air absorbs more moisture)
- Wind is present (carries water vapor away from surface)
How much water evaporates?
In Portugal’s summer conditions (June-September), uncovered pools typically lose:
- Coastal regions (Lisbon, Porto, Algarve coast): 4-6mm per day
- Inland regions (Alentejo, Beira Interior, Trás-os-Montes): 6-10mm per day during heatwaves
For a standard 8m x 4m pool (32m² surface area):
- 6mm daily evaporation = 192 liters per day = 5,760 liters per month
- 10mm daily evaporation = 320 liters per day = 9,600 liters per month
Over a four-month summer, that’s 23,000-38,000 liters lost to evaporation alone if the pool remains uncovered.
Secondary Water Losses
Backwashing filters: Sand and DE filters require periodic backwashing (reverse-flushing to clean the filter media). Each backwash uses 200-500 liters depending on pool size and filter type. Monthly backwashing adds 2,400-6,000 liters annually.
Splashing and swimmer carryout: Swimmers splash water out and carry it on their bodies when exiting. This is minimal with 50-150 liters per pool party or heavy use day, and shouldn’t be a conservation priority.
Leaks: Undetected leaks can waste far more water than evaporation. A small crack or fitting leak losing 2mm per day wastes 64 liters daily (1,920 liters monthly). They are often unnoticed until the water bill arrives.
Pool Covers: The Most Effective Conservation Measure
Pool covers reduce evaporation by 70-95% depending on cover type, making them the single most impactful investment for water conservation.
Types of Pool Covers and Effectiveness
Solid safety covers (95% reduction):
Heavy-duty covers that completely seal the pool surface. Block all sunlight, prevent debris entry, and provide maximum evaporation reduction.
Pros: Maximum water savings, child/pet safety barrier, prevent algae growth (no sunlight)
Cons: Heavy (require mechanism or effort to remove), expensive (€1,000-€5,000 depending on pool size)
Solar covers / bubble covers (70-85% reduction):
Lightweight plastic sheets with air bubbles that float on the water surface. Allow some sunlight through while reducing evaporation and retaining heat.
Pros: Affordable (€100-€400), warm pool water, easy to deploy and remove manually
Cons: Less durable (1-3 year lifespan), don’t provide safety barrier, can be cumbersome to handle daily
Liquid pool covers (40-50% reduction):
Chemical products that create an invisible molecular layer on the water surface, reducing evaporation without physical barriers.
Pros: No handling required, works 24/7, minimal impact on pool use
Cons: Least effective reduction, ongoing cost (reapply every 2-4 weeks), swimmers temporarily disrupt the layer
Mesh covers (50-70% reduction):
Breathable covers that allow water to pass through but block debris and reduce evaporation.
Pros: Won’t collect standing water (important in rainy regions), safer than solid covers in some circumstances
Cons: Less effective than solid covers, some evaporation still occurs
Cover Best Practices
Use covers overnight: Even if removing daily for swimming, covering overnight (roughly 12 hours) when evaporation continues reduces water loss by 35-50%. This is manageable even with manual covers.
Cover during heat waves: When temperatures exceed 35°C and humidity is very low, evaporation accelerates dramatically. Covering during peak afternoon heat (14:00-18:00) helps even if the pool is in active use.
Combine solar and solid covers: Use solar covers during swimming season (warm water, moderate evaporation reduction) and switch to solid safety covers during off-season or extended periods of non-use.
Portugal-specific consideration: In coastal areas with high summer tourist traffic, pools often remain in constant use. Partial covering (overnight only) provides savings without interfering with daytime swimming.
Filter Type and Backwashing
The type of filtration system significantly affects water consumption during drought.
Sand and DE Filters: High Water Use
Sand filters and diatomaceous earth (DE) filters require regular backwashing which is reversing water flow to flush accumulated debris from the filter media.
Water consumption:
- Each backwash: 200-500 liters
- Frequency: Weekly to monthly depending on pool use and debris load
- Annual total: 2,400-6,000 liters wasted
During drought with water restrictions, this creates a dilemma: backwash and waste water, or skip backwashing and risk poor filtration.
Cartridge Filters: Zero Backwash Waste
Cartridge filters use pleated fabric filters that are manually removed, hosed off, and reinstalled. No backwashing required.
Water savings:
- 3,000-6,000 liters annually (eliminated backwash waste)
- Cleaning cartridges uses 20-50 liters (brief hosing)
- Net savings: 95%+ reduction in filter-related water use
Why cartridge filters aren’t universal:
They require more physical labor (removing, cleaning, reinstalling cartridges every 2-4 weeks) and have higher upfront filter replacement costs (€50-150 per cartridge annually vs. minimal cost for sand/DE media). However, during drought, the water savings justify the extra effort.
Converting from sand/DE to cartridge:
Possible for many pools. Requires new filter housing and pump adjustments (€400-€1,200 installation). Payback period is 3-5 years under normal conditions but accelerates during drought if water restrictions or surcharges apply.
Chemistry Management to Avoid Draining
Properly balanced water chemistry prevents the need to drain and refill pools — the single largest water waste event in pool maintenance.
Why Pools Are Drained
Total Dissolved Solids (TDS) accumulation: Over time, minerals, chemicals, and contaminants accumulate in pool water. When TDS exceeds 1,500-2,000 ppm above tap water baseline, water becomes difficult to balance.
Calcium hardness buildup: In areas with hard tap water (common throughout Portugal), calcium accumulates with each refill, eventually causing scale formation.
Cyanuric acid (CYA) buildup: Stabilized chlorine products add CYA, which accumulates and eventually reduces chlorine effectiveness.
Traditionally, the solution is draining 50-100% of pool water and refilling with fresh water. For a 40,000-liter pool, that’s 20,000-40,000 liters wasted and unacceptable not only during drought.
Strategies to Extend Water Life
Minimize stabilized chlorine use: Use liquid chlorine (sodium hypochlorite) or saltwater chlorine generators instead of dichlor or trichlor tablets. These don’t add CYA, preventing one major buildup issue.
Monitor and balance aggressively: Test water weekly (not monthly). Small corrections prevent major imbalances that eventually require dilution.
Use sequestering agents for calcium: Chemicals that bind calcium and prevent scale formation allow you to tolerate higher hardness levels without draining.
Accept higher TDS during drought: Water with TDS 500-1,000 ppm above normal is still swimmable and safe. It may require more frequent chemistry adjustments, but this is preferable to draining.
Partial water replacement instead of full drains: If chemistry becomes unmanageable, drain 25% and refill rather than emptying the entire pool. This dilutes contaminants while conserving water.
Portugal note: Many Portuguese municipalities have hard water (200-300 ppm calcium hardness). This makes calcium buildup a recurring challenge, but sequestering agents and accepting slightly cloudier water during drought extends water life significantly.
Leak Detection and Repair
Leaks waste more water than any other source, and they’re often silent, going undetected for months.
How to Detect Leaks
Bucket test (simple DIY method):
- Fill a bucket 3/4 full and place it on the pool steps (weighted to prevent tipping)
- Fill the bucket so water level inside matches pool water level outside
- Mark both water levels
- Wait 24 hours with pool pump off
- Compare water level drops: If pool lost significantly more water than bucket, you have a leak
Acceptable water loss: 2-3mm per day in hot, dry conditions is normal evaporation. More than 5mm daily suggests a leak.
Professional leak detection: Companies use specialized equipment (pressure testing, acoustic listening devices, dye tests) to locate leaks in underground plumbing, structural cracks, or equipment. Cost: €150-€400, worth it if losing significant water.
Common Leak Sources
- Pump/filter connections and seals (most common, usually easy to fix)
- Skimmer or return fittings (cracks develop over time)
- Underground plumbing (hardest to locate and repair)
- Pool structure cracks (concrete pools are most vulnerable)
A small leak, just 1mm per day, wastes 32 liters daily, 960 liters monthly, or 3,840 liters over a four-month summer. That exceeds typical swimmer splashing and carryout by 20-40 times.
Fix leaks immediately during drought. The repair cost (€100-€500 for most leaks) pays for itself in water savings within weeks.
Operational Adjustments During Drought
Reduce Water Temperature
Warmer water evaporates faster. If your pool is heated:
- Lower thermostat setting from 28°C to 25-26°C (still comfortable for swimming)
- Turn off heating entirely during peak drought if temperatures are already warm
- Use solar covers to retain heat naturally rather than active heating
Water savings: Lowering temperature by 3°C can reduce evaporation by 15-25%.
Turn Off Water Features
Waterfalls, fountains, deck jets, and spillover spas increase water surface area exposed to air, accelerating evaporation.
Typical water loss from features:
- Small fountain: 50-100 liters per day
- Waterfall: 100-300 liters per day
- Spillover spa (constantly running): 200-500 liters per day
During drought, turn these features off except for occasional use. The aesthetic loss is temporary; the water savings are substantial.
Adjust Pool Water Level
Maintaining water at the midpoint of the skimmer opening is standard practice, but during drought you can lower levels slightly (1-2cm below normal) without affecting filtration. This reduces exposed surface area at the waterline where evaporation is highest.
Don’t over-lower: Water must reach the skimmer to function properly. Dropping levels too far prevents skimming and strains the pump.
Water Restrictions and Compliance in Portugal
Many Portuguese municipalities implement water restrictions during drought, particularly in Alentejo, Algarve, and Beira Interior.
Common Restrictions
Level 1 (voluntary conservation):
- Encouragement to reduce non-essential water use
- Public awareness campaigns
- No mandatory limits
Level 2 (moderate restrictions):
- Limited pool refilling (often 1 time per season, or maximum X cubic meters per month)
- Banned hosing of outdoor surfaces
- Restricted irrigation schedules
- Possible surcharges for high consumption
Level 3 (severe restrictions):
- Pool refilling may be completely banned
- Topping off for evaporation replacement may be restricted to specific days/times
- Significant fines for violations
How to Comply
Top off during permitted hours: If restrictions limit when you can add water, run a hose timer during approved windows (often nighttime to reduce grid strain).
Document consumption: Keep records of water added, evaporation rates, and conservation measures. If questioned, you can demonstrate responsible use.
Communicate with municipality: Some regions allow exemptions for pools with covers or efficient systems. Proactively contacting water authorities and explaining your conservation measures may provide flexibility.
Consider partial seasonal closure: If restrictions are severe and you can’t maintain water levels, partially draining (to 50% capacity) and covering the pool preserves structure while dramatically reducing evaporation. Refill when restrictions ease.
Natural Pools: Built-In Drought Resilience
Natural swimming pools, designed with biological filtration using aquatic plants instead of mechanical filters and chemicals, have inherent drought advantages over conventional pools.
Lower evaporation rates: The regeneration zone (planted area) provides shade over 30-50% of total water surface, reducing overall evaporation by 20-40% compared to fully exposed conventional pools.
No backwashing: Natural pools use settlement zones and gentle circulation, not pressurized filters that require backwashing. This eliminates 3,000-6,000 liters of annual waste.
Biological balance tolerates lower water levels: Natural pools can operate at reduced levels (15-20% below normal) during drought without chemistry failures because the ecosystem self-regulates. Conventional pools struggle with chemistry when water levels drop significantly.
Rainwater integration: Natural pools easily incorporate rainwater harvesting from roofs or surfaces. The planted zones purify incoming water naturally, making rainwater supplementation simple and safe.
Lower operating costs during drought: No chemicals to purchase, no backwash water waste, reduced pump energy (gentler circulation rather than high-pressure filtration). Total water use is typically 40-60% less than conventional pools annually.
If you’re planning a new pool in a drought-prone region of Portugal, or considering converting an existing conventional pool, a natural pool designed for local climate conditions provides both water conservation and lower ongoing costs.
Oásis Biosistema specializes in natural pool design optimized for Portugal’s Mediterranean climate, including drought-resilient systems that minimize water consumption while maintaining beautiful, swimmable water year-round.
Putting It in Perspective: Pools vs. Lawns
The common perception is that pools waste enormous amounts of water. The reality: well-maintained pools use less water than lawns of equivalent size.
Typical lawn water consumption (Portugal summer):
An 8m x 4m lawn (32m²) requires:
- 15-25 liters per m² per week (hot, dry conditions)
- 480-800 liters per week for 32m² lawn
- 1,920-3,200 liters per month
- 7,680-12,800 liters over four-month summer
Typical pool water consumption (same size, 8m x 4m):
Uncovered pool:
- 5,760-9,600 liters per month evaporation
- 200-500 liters per month backwashing (if applicable)
- 23,000-40,000 liters over four months
Covered pool (70% evaporation reduction):
- 1,728-2,880 liters per month evaporation
- 0 liters backwashing (cartridge filter)
- 6,912-11,520 liters over four months
Conclusion: A covered pool with cartridge filter uses approximately the same water as a lawn of equivalent size, and provides far more value (cooling, recreation, family bonding, exercise) than ornamental grass.
An uncovered pool uses more water than a lawn, but not dramatically so, and unlike lawns, pools provide functional value year-round rather than being purely aesthetic.
Conclusion
Summer drought doesn’t mean abandoning your pool. With strategic conservation measures like covers to reduce evaporation, cartridge filters to eliminate backwash waste, proper chemistry to avoid draining, leak detection and repair, and operational adjustments like turning off water features, you can maintain clean, safe, swimmable water while using minimal water.
The key principles:
- Cover the pool (70-95% evaporation reduction)
- Eliminate backwashing (switch to cartridge filters if possible)
- Maintain perfect chemistry (balanced water lasts indefinitely)
- Find and fix leaks immediately
- Adjust operations (lower temperature, turn off features)
These measures combined can reduce summer water consumption by 50-80% compared to standard pool operation, making pool ownership compatible with responsible water use even during severe drought.
Portugal’s summers are getting hotter and drier. Planning for drought isn’t pessimism; it’s prudent management. Implement these conservation practices before restrictions arrive, and your pool becomes a sustainable part of your property rather than a water liability.
FAQ
Is September too early to close the pool?
September is usually not too early to close your pool, especially in cooler climates. A good rule is to close it when temperatures consistently drop below 15°C (60°F). Closing too early in warm weather can lead to algae growth and more work when reopening.
What are the 3 C’s of pool maintenance?
The 3 C’s of pool maintenance are Cleaning, Circulation, and Chemistry. Cleaning removes debris, circulation keeps water moving through the filter, and chemistry ensures proper balance of pH, chlorine, and alkalinity for safe, clear water.
Do you need to shock your pool after every rain?
You don’t always need to shock your pool after light rain, but it’s recommended after heavy rain. Rain can dilute chemicals and introduce contaminants, so testing the water and adding shock if chlorine levels drop helps keep the pool clean and safe.
How to maintain a pool during summer?
In summer, maintain your pool by skimming daily, vacuuming weekly, and checking chemicals 2–3 times per week. Run the filter longer (8–12 hours daily), keep chlorine and pH balanced, and shock the pool regularly to prevent algae and bacteria growth.
