What size water tank do I need for my home in Jamaica?

A typical Jamaican household of 4 people uses approximately 320 gallons per day (80 gal/person). With 5 days of storage for NWC supply interruptions, you would need a 1,600 gallon tank minimum. We recommend the next standard size up: 2,000 gallons. Use our calculator for an accurate estimate based on your specific needs.

How much rainwater can I collect from my roof in the Caribbean?

Rainwater collection depends on your roof area, local rainfall, and collection efficiency. A 1,500 sq ft roof in Kingston, Jamaica (32 inches annual rainfall) can collect approximately 22,000 gallons per year at 80% efficiency. Portland, Jamaica (90 inches) could yield over 60,000 gallons from the same roof.

What pump size do I need for my water tank?

Pump sizing depends on the elevation head (height the water must be pumped) and desired flow rate. A typical residential installation with 20 ft elevation and 10 GPM flow rate requires a 0.5-0.75 HP pump. Our calculator accounts for friction losses and pump efficiency to recommend the right size.

Water Tank Sizing Calculator - Caribbean Water Storage & Rainwater Harvesting

New to this? Plain-English guide

Catchment Area — the roof area that collects rain. Only the footprint facing the sky counts, and every square foot collects about 0.6 gallons per inch of rainfall.

Days of Storage — how many days your tanks should supply the household with no rain or mains water. Hurricane-season planning usually calls for more.

First Flush Diverter — a fitting that discards the first dirty water off the roof each time it rains (dust, leaves, bird droppings) before clean water enters the tank.

Collection Efficiency — the share of rainfall that actually makes it into the tank after evaporation, splashing, and overflow. Typically 75-90%.

Sizing Method

Building Type

Number of Occupants

Daily Usage per Person (gal)

Days of Storage

3–5 days for reliable supply areas. 7–14 days where NWC supply is intermittent.

Units

Currency

Water Cost per Gallon

Tank Type

Pump Required

Project Management

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Calculation Method: Occupancy mode sizes tanks based on daily demand and days of storage. Rainwater mode calculates annual catchment potential from roof area and local rainfall, with monthly surplus/deficit analysis using Caribbean wet/dry season distribution.

WattWorks Design - Caribbean Water Systems: Serving Jamaica and the Caribbean with water storage design, rainwater harvesting systems, and plumbing engineering. Need a detailed water system design? Visit WattWorks Design

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Water Storage Guide

Water Storage Basics
Water tanks should be sized to bridge the gap between supply and demand. In the Caribbean, intermittent municipal supply (NWC in Jamaica, WASA in Trinidad) makes adequate storage essential. A minimum of 3 days supply is recommended; 5–7 days is standard for areas with unreliable service.

Rainwater Harvesting in the Caribbean
Caribbean rainfall is highly seasonal. The wet season (June–November) delivers approximately 65% of annual rainfall, while the dry season (December–May) provides only 35%. Effective rainwater harvesting requires a tank large enough to store wet season surplus for dry season use. Roof material, guttering condition, and first flush diversion all affect collection efficiency.

Tank Material Comparison

Material

Pros

Cons

Polyethylene

Lightweight, affordable, UV-resistant

Limited sizes, shorter lifespan

Concrete

Durable, any size, keeps water cool

Heavy, expensive, may crack

Steel

Strong, large capacities

Corrosion risk, expensive

Fiberglass

Corrosion-free, lightweight

Expensive, UV degradation

Pump Sizing Basics
Pump size depends on total dynamic head (elevation + friction losses) and desired flow rate. Friction losses are estimated at approximately 5% of elevation head for typical residential piping. Pump efficiency is typically 60% for small centrifugal pumps. Standard pump sizes: 0.5, 0.75, 1.0, 1.5, 2.0, 3.0, and 5.0 HP.

Caribbean Water Supply Context
Many Caribbean islands face chronic water supply challenges. Jamaica's NWC (National Water Commission) provides piped water to approximately 70% of the population, but supply is often intermittent — sometimes as little as 2–3 days per week in some areas. Trinidad's WASA faces similar challenges. Private water storage is not optional but essential for continuity of supply. Rainwater harvesting supplements municipal supply and reduces dependence on trucked water during droughts.

Disclaimer: This calculator provides estimates for preliminary tank sizing. Actual requirements depend on site-specific conditions including local water supply reliability, rainfall patterns, and plumbing configuration. Always consult a qualified plumbing engineer for detailed system design.

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