Rainwater Storage Tank Size Comparison
Choosing the right storage tank is one of the most important decisions in a rainwater harvesting system. Too small, and you lose water to overflow during heavy rain events. Too large, and you overspend on capacity you will never fill. Below we compare 12 storage options ranging from a basic 55-gallon rain barrel to a 10,000-gallon cistern, covering capacity, material, cost, dimensions, and ideal use cases for each.
All Tank Sizes at a Glance
The table below provides a quick comparison of every tank size in our database. Click any tank name for a detailed page covering installation, maintenance, ideal roof area pairings, and cost-per-gallon analysis. Costs reflect typical retail prices for the tank itself — installation, plumbing, pump systems, and foundation work are additional expenses that scale with tank size.
| Tank | Capacity | Material | Dimensions | Cost Range | Cost/Gallon |
|---|---|---|---|---|---|
| 55-Gallon Rain Barrel | 55 gal | Plastic (HDPE) | 24" diameter x 35" tall | $50-$120 | $0.91-$2.18 |
| 100-Gallon Rain Barrel | 100 gal | Plastic (HDPE) | 30" diameter x 38" tall | $80-$180 | $0.80-$1.80 |
| 200-Gallon Slim Tank | 200 gal | Plastic (LLDPE) | 60" tall x 48" wide x 16" deep | $200-$400 | $1.00-$2.00 |
| 275-Gallon IBC Tote | 275 gal | HDPE in Steel Cage | 48" x 40" x 46" | $100-$200 | $0.36-$0.73 |
| 500-Gallon Storage Tank | 500 gal | Polyethylene | 46" diameter x 60" tall | $300-$600 | $0.60-$1.20 |
| 1,000-Gallon Storage Tank | 1,000 gal | Polyethylene | 64" diameter x 62" tall | $500-$900 | $0.50-$0.90 |
| 1,000-Gallon Underground Tank | 1,000 gal | Underground Polyethylene | 72" x 56" x 48" (buried) | $800-$1,500 | $0.80-$1.50 |
| 1,500-Gallon Storage Tank | 1,500 gal | Polyethylene | 87" diameter x 58" tall | $700-$1,200 | $0.47-$0.80 |
| 2,500-Gallon Storage Tank | 2,500 gal | Polyethylene | 95" diameter x 72" tall | $1,000-$1,800 | $0.40-$0.72 |
| 5,000-Gallon Storage Tank | 5,000 gal | Polyethylene or Fiberglass | 102" diameter x 120" tall | $2,000-$4,000 | $0.40-$0.80 |
| 5,000-Gallon Underground Tank | 5,000 gal | Underground Polyethylene or Fiberglass | 12' x 6' x 5' (buried) | $4,000-$8,000 | $0.80-$1.60 |
| 10,000-Gallon Cistern | 10,000 gal | Concrete or Polyethylene | 12' diameter x 12' tall (varies) | $5,000-$10,000 | $0.50-$1.00 |
How to Choose the Right Tank Size
Your ideal tank size depends on three factors: your monthly harvest volume, your monthly water demand, and the rainfall distribution in your area. The goal is to capture enough water during wet months to sustain your needs through dry periods without excessive overflow losses.
Step 1: Calculate your monthly harvest. Use our calculator to see how much water your roof produces each month based on your location and roof specifications.
Step 2: Determine your monthly demand. Add up the daily water requirements for all your intended uses and multiply by the number of days in the month. Remember that seasonal uses like garden irrigation only apply during the growing season.
Step 3: Find your largest surplus month. The month with the biggest gap between harvest and demand tells you how much storage you need. Your tank should be at least large enough to hold this surplus, preventing overflow and waste.
As a quick rule of thumb: for garden-only use, start with a 55-100 gallon rain barrel. For dedicated garden irrigation, upgrade to 500-1,000 gallons. For whole-property outdoor use or indoor non-potable use, plan for 1,500-5,000 gallons. For primary water source applications (rural homes, farms), consider 5,000-10,000 gallons.
Tank Categories Explained
Entry-Level: Rain Barrels (55-275 gallons)
Rain barrels are the entry point to rainwater harvesting. They are inexpensive ($50-200), easy to install without professional help, and require no pump or plumbing modifications. A single barrel connects to one downspout and fills quickly during even moderate rain events — a 1,000-square-foot roof produces about 30 gallons from half an inch of rain. Rain barrels are ideal for watering container plants, small garden beds, and general outdoor tasks. Their limitations are storage capacity (a single barrel may only last a day or two of garden watering) and water pressure (gravity-fed flow is low without elevation). Many homeowners start with a barrel and upgrade as they experience the benefits.
Mid-Range: Storage Tanks (500-2,500 gallons)
Storage tanks in the 500-2,500 gallon range serve homeowners with serious irrigation needs or those who want to offset a meaningful portion of their outdoor water consumption. These tanks require a level foundation (concrete pad or compacted gravel), proper inlet and overflow plumbing, and typically a pump for adequate water pressure. The investment is higher ($300-1,800 for the tank alone) but the payback is proportionally greater. A 1,000-gallon tank paired with a 1,500-square-foot roof in a 40-inch rainfall area can supply most of a vegetable garden's annual irrigation needs. At this scale, accessories like first-flush diverters, leaf screens, and tank-level gauges become worthwhile additions.
Large-Scale: Cisterns & Underground Tanks (5,000-10,000 gallons)
Large cisterns and underground tanks are for properties where rainwater harvesting is a primary water strategy — rural homes, small farms, commercial buildings, or drought-prone areas. Installation is a professional project involving heavy equipment, engineered foundations, and complex plumbing. The costs are significant ($2,000-10,000+ for the tank) but so are the benefits: a 10,000-gallon cistern connected to a 3,000-square-foot roof in a 40-inch rainfall area captures over 55,000 gallons annually, providing meaningful water independence. Underground tanks offer the advantage of invisible storage and freeze protection but cost more to install due to excavation requirements.
Understanding Tank Costs
The cost per gallon of storage decreases as tank size increases. A 55-gallon rain barrel costs $0.91-$2.18 per gallon of capacity, while a 10,000-gallon cistern costs just $0.50-$1.00 per gallon. However, larger tanks come with additional installation costs that smaller barrels avoid: foundation work, plumbing connections, pumps, pressure tanks, and potentially excavation for underground models. A complete 1,000-gallon above-ground system (tank, pump, first-flush diverter, plumbing, and foundation) typically costs $1,500-$3,000 installed. A 5,000-gallon underground system can run $8,000-$15,000 including excavation and backfill.
To estimate your payback period, divide your total system cost by your annual water savings. In areas with high water rates ($0.01-$0.015 per gallon), a system harvesting 20,000 gallons per year saves $200-$300 annually, paying for a rain barrel setup in under a year or a mid-range tank system in 5-10 years. In low-rate areas, the financial payback is longer, but the environmental and resilience benefits remain.