🎯 Why Reservoir Sizing Matters
Water is life, but water availability doesn’t always match water demand. Whether you’re designing a municipal water system, a rainwater harvesting cistern, or an industrial process buffer tank, one fundamental challenge remains: supply and demand rarely happen at the same time.
Building an oversized tank wastes money on concrete and land. An undersized tank leads to water shortages and system failure. The Reservoir Optimizer Pro solves this problem using proven hydraulic engineering principles.
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Instant Calculations
Real-time simulation using the industry-standard Mass Curve (Ripple) method with hourly precision.
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Visual Analytics
Interactive charts showing tank levels, overflow events, and deficit periods throughout the day.
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Professional Reports
Export to PDF, Word, or CSV for client presentations and engineering documentation.
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Flexible Inputs
Support for constant or variable flows, multiple time resolutions, and custom safety factors.
🔧 How the Tool Works
The Reservoir Optimizer Pro uses a sophisticated hydraulic simulation engine that tracks water flow hour-by-hour, daily, weekly, or monthly to determine the exact storage capacity needed to balance supply and demand.
💡 Core Concept
The tool calculates cumulative surplus and deficit throughout your chosen time period. The required tank capacity equals the maximum difference between what flows in and what flows out.
📋 Step-by-Step Guide
Define Your Water Source (Inflow)
Choose between Constant (steady 24/7 flow like a spring or municipal pipe) or Varying (intermittent supply like solar pumps or scheduled city water).
Example: A solar pump delivers 8 m³/h but only operates from 9 AM to 5 PM. Use “Varying” mode and set flow to 0 outside those hours.
Define Water Consumption (Outflow)
Enter your demand pattern using one of three methods:
- Percentage Distribution: Best for typical scenarios. Set total daily demand (e.g., 120 m³) and distribute it across hours using sliders.
- Direct Input: Enter exact flow rates if you have logged data.
- Factor Mode: Use multipliers of average demand (e.g., 2.0× during peak hours).
Configure Simulation Settings
Set the Time Resolution (hourly recommended), Safety Factor (10-20% for reliability), and Starting Level (usually 50% or 100%).
Analyze Results
Review the “Calculated Optimum” capacity. Check the analysis chart to ensure the tank never runs dry and overflow events are acceptable. Adjust inputs to optimize.
Export Documentation
Generate professional reports using the PDF or Word export buttons. Share with clients, contractors, or regulatory authorities.
📐 The Mass Curve Method Explained
This tool implements the Ripple Diagram Method, developed by W. Ripple in 1883 and still the industry standard for reservoir sizing. It’s based on a simple but powerful principle:
How It Works Mathematically
At every time step (hour), the algorithm calculates:
- Cumulative Inflow: Total water supplied from time 0 to hour i
- Cumulative Outflow: Total water consumed from time 0 to hour i
- Mass Balance: Difference = Cumulative Inflow – Cumulative Outflow
When this difference is positive, you have a surplus (tank fills). When negative, you have a deficit (tank empties). The capacity must be large enough to contain the maximum surplus while never letting the deficit exceed the available stored water.
⚠️ Critical Assumption
The Mass Curve assumes your input data represents a design day or worst-case scenario. If your actual demand exceeds the design, the tank will fail. Always use conservative estimates or safety factors.
🌍 Real-World Examples
The Challenge: The pump only works during sunlight (8 hours), but people need water at dawn and dusk when the pump is off.
Configuration in Tool:
- Supply Pattern: Varying → 15 m³/h from 09:00-17:00, 0 m³/h otherwise
- Demand Pattern: 35% at 06:00-08:00, 10% midday, 40% at 17:00-19:00
- Safety Factor: 15% (moderate reliability)
✓ Result: Calculated optimum capacity = 87 m³. The tank fills during sunlight hours and drains during morning/evening peaks. Total inflow (120 m³) exceeds total outflow (120 m³), creating a sustainable system with a 15% safety buffer.
The Challenge: Spring flow is slow but reliable. Guest showers and cooking create sharp demand spikes that exceed instantaneous supply.
Configuration in Tool:
- Supply Pattern: Constant → 2.5 m³/h (60 m³/day total)
- Demand Pattern: Sharp peaks at breakfast/dinner times, minimal at night
- Safety Factor: 10% (spring is very reliable)
✓ Result: Calculated optimum capacity = 18 m³. The tank slowly refills during low-demand periods (especially 10 PM – 6 AM) and depletes during guest activity peaks. Net balance is positive (+10 m³/day surplus), providing resilience.
The Challenge: City water only flows for 3 hours per day, but the factory runs for 12 hours. Production cannot stop.
Configuration in Tool:
- Supply Pattern: Varying → 70 m³/h from 05:00-08:00 (210 m³ total), 0 otherwise
- Demand Pattern: 16.7 m³/h from 06:00-18:00 (200 m³), 0 at night
- Safety Factor: 25% (city supply unreliable, production critical)
✓ Result: Calculated optimum capacity = 142 m³. Tank fills rapidly during the 3-hour city supply window, then gradually empties throughout the 12-hour production shift. With 25% safety factor, final recommended capacity = 178 m³ to account for supply interruptions.
The Challenge: Municipal water is only available for 3 hours each morning (6-9 AM). The family needs water throughout the day for showers, cooking, laundry, toilet flushing, and evening activities.
Typical Daily Usage Pattern:
- 6-8 AM: Morning showers, breakfast prep (30% of daily usage)
- 8 AM-12 PM: Laundry, cleaning (15% of daily usage)
- 12-2 PM: Lunch preparation, dishes (10% of daily usage)
- 2-6 PM: Light usage (10% of daily usage)
- 6-9 PM: Dinner prep, evening showers, dishes (30% of daily usage)
- 9 PM-6 AM: Minimal usage, toilet flushing (5% of daily usage)
Configuration in Tool:
- Supply Pattern: Varying → 300 L/h from 06:00-09:00 (900L total), 0 L/h otherwise
- Demand Pattern: Peaks at 06:00-08:00 (240L) and 18:00-21:00 (240L), distributed throughout day
- Time Resolution: Hourly (24 hours)
- Safety Factor: 15% (account for supply interruptions or guests)
✓ Result: Calculated optimum capacity = 560 Liters. The tank fills rapidly during the 3-hour municipal supply window (900L input). Water is consumed throughout the day with peaks during morning and evening. The tank empties to its lowest point around 8-9 PM after evening activities, then refills the next morning. With 15% safety factor, recommended tank size = 650L (round up to standard 700L or 1000L tank).
The Challenge: All rainfall occurs in 4 months, but water is needed year-round. Must store water from wet season to last through 8 dry months.
Configuration in Tool:
- Time Step: Monthly (12 periods)
- Supply Pattern: 55 m³/month for Jun-Sep, 0 for Oct-May
- Demand Pattern: 15 m³/month constant throughout year
- Safety Factor: 20% (account for drought years)
✓ Result: Calculated optimum capacity = 125 m³. The cistern fills completely during monsoon months, then slowly depletes through the dry season. Net annual balance is positive (+40 m³), allowing the system to recover during wet years.
🎯 Optimization Strategies
Building a water tank is expensive. Here’s how to minimize costs while maintaining reliability:
Strategy 1: Peak Shaving
The single most effective way to reduce tank size is to flatten your demand curve. Spread water consumption more evenly throughout the day instead of concentrating it in narrow peaks.
💡 Example
A hotel that runs laundry, irrigation, and pool filling at 7 AM (same time as guest showers) might need a 50 m³ tank. By shifting laundry to midnight and irrigation to 2 AM, the required capacity drops to 28 m³—a 44% savings.
Strategy 2: Supply Schedule Alignment
If you control the supply (like a pump), schedule it to match demand patterns. Don’t pump water at 3 AM if nobody uses it until 7 AM—you’re just filling the tank unnecessarily.
Strategy 3: Dual-Source Systems
Combine a small continuous source (like a spring) with a larger intermittent source (like city water). The continuous source handles baseline demand, reducing the burst capacity needed from the intermittent source.
Strategy 4: Safety Factor Tuning
Don’t over-engineer. Use appropriate safety factors based on consequence of failure:
- 5-10%: Highly reliable sources, non-critical applications
- 15-20%: Standard municipal/commercial projects
- 25-30%: Critical infrastructure (hospitals, data centers)
- 40-50%: Emergency reserves, disaster scenarios
🔍 Common Issues & Solutions
⚠️ Net Deficit (System Unsustainable)
Symptom: Net Balance shows negative value (red indicator)
Cause: Total demand exceeds total supply over the time period
Solution: Increase supply capacity, reduce demand, or implement rationing. No amount of storage can fix this—you’re using more water than you have.
⚠️ Tank Runs Dry (Hits 0%)
Symptom: Analysis chart shows tank level reaching zero
Cause: Selected capacity is smaller than calculated optimum, or starting level too low
Solution: Click “Set Optimum” button, or increase safety factor, or set starting level to 100%
💡 Constant Overflow
Symptom: Tank stays at 100% most of the day
Cause: Supply significantly exceeds demand, or tank is oversized
Solution: This isn’t necessarily a problem, but you may be wasting pump energy. Consider reducing pump hours or installing overflow controls.
❓ Frequently Asked Questions
What’s the difference between “Calculated Optimum” and “Selected Capacity”?
Calculated Optimum is the exact mathematical minimum required. Selected Capacity is what you actually build (usually rounded up to standard tank sizes like 5,000L, 10,000L, 15,000L). You typically select a capacity equal to or slightly larger than the optimum.
Can I use this for monthly or yearly calculations?
Yes! Change the “Time Step” in Reservoir Config to “Monthly” for seasonal storage (like rainwater harvesting) or “Daily” for weekly patterns. The Mass Curve method works at any time scale.
Why does the tool recommend such a large tank?
If supply and demand are severely misaligned (e.g., solar pump active 8 hours but demand is 24 hours), you need to store nearly a full day’s worth of water. Review your supply pattern—shifting pump hours to match demand can dramatically reduce required capacity.
What if I have multiple sources (well + city water)?
Add them together in the Supply Pattern. If your well provides 2 m³/h continuously and city water adds 10 m³/h from 5-8 AM, your supply profile would be 2 m³/h baseline with a spike to 12 m³/h during those 3 hours.
Does this account for evaporation or leakage?
No. The tool calculates hydraulic flow only. For open tanks, manually subtract evaporation from your Supply input (typically 5-10 mm/day depending on climate). For leakage, reduce supply by the estimated loss percentage.
What’s a good starting level for simulations?
Use 100% if your tank fills overnight (typical for residential). Use 50% for steady-state analysis. Use 0% if you want to test worst-case startup scenarios.
Can I model a tank that serves multiple buildings?
Yes. Simply sum the demand from all buildings in your Demand Pattern. For example, if Building A needs 30 m³/day and Building B needs 50 m³/day, enter a total demand of 80 m³/day.
How accurate is the Mass Curve method?
It’s the industry-standard technique used globally since 1883. Accuracy depends on the quality of your input data. Use measured flow data or conservative design estimates for best results.
Does this calculate pipe sizes or pump power?
No. This tool only sizes storage capacity. Pipe sizing requires friction loss calculations (Hazen-Williams or Darcy-Weisbach equations), and pump sizing requires total dynamic head analysis—both are separate hydraulic disciplines.
Is my data saved on a server?
No. All calculations run in your browser. Your data never leaves your device. Use the “Save” button to download a .json file to your computer for future sessions.
What units are supported?
The tool supports Liters (L), Gallons (Gal), and Cubic Meters (m³) for volume. For time resolution, you can choose Seconds, Minutes, Hours, Days, Weeks, or Months depending on your analysis needs.
Can I print the reports?
Yes. Click “PDF Report” for a professional print-ready document, or “Word Report” for editable documentation. Both include all charts, calculations, and configuration details.
Reservoir Optimizer Pro is a free professional tool for hydraulic engineers, planners, and students.
Based on the Ripple Diagram Method (W. Ripple, 1883) | Developed for educational and professional use