Types of Cistern: Essential Guide

Understanding different types of cisterns is key for efficient water storage. From traditional underground tanks to modern modular options, each serves specific needs for rainwater harvesting, backup water supply, or agricultural use. Choosing the right cistern ensures durability, capacity, and suitability for your property and goals.

A cistern is essentially a water storage tank, often used for collecting rainwater or providing an emergency water supply. If you’ve ever wondered why some homes have large tanks buried underground or others have sleek, visible containers, you’re looking at different types of cisterns! These can seem a bit bewildering at first, but they are simpler than you think. Knowing the right type for your needs can save you hassle and ensure a reliable water source. Let’s break down the world of cisterns so you can confidently choose the best one for your situation. We’ll explore what makes them different and how they work.

Why You Need to Know About Cistern Types

Having a reliable water supply is crucial, whether it’s for your home, garden, or business. Cisterns offer a fantastic way to store water, especially in areas where municipal water pressure is low, unreliable, or non-existent. They are also a cornerstone for sustainable living, allowing you to harness rainwater instead of relying solely on treated sources. But not all cisterns are created equal.

The landscape is varied, with different materials, shapes, and installation methods designed for specific purposes. Picking the wrong type could mean a tank that’s too small, leaks, isn’t durable enough for your climate, or simply isn’t cost-effective. This guide will help you navigate these options, ensuring you make an informed decision for your water storage needs. We’ll cover everything from the traditional to the cutting-edge.

Understanding the Basics: What is a Cistern?

At its heart, a cistern is a watertight tank built to hold water. The term “cistern” is primarily used for tanks that store potable (drinkable) or non-potable water collected from sources like rainwater, wells, or springs. Unlike a simple water barrel, cisterns are often larger and are designed for long-term storage and integration into a property’s water system via pumps and filtration. They can be made from various materials and installed above ground, below ground, or even within a building’s structure. The primary purposes include:

• Rainwater Harvesting: Collecting precipitation from rooftops for later use in irrigation, flushing toilets, or even drinking after proper treatment. This is a fantastic way to reduce your reliance on mains water and be more environmentally friendly.
• Emergency Water Supply: Providing a backup water source during power outages or disruptions to the municipal water supply. This offers peace of mind and ensures essential needs are met.
• Low Water Pressure Solutions: Storing water at a higher elevation to provide gravity-fed pressure, or using a pump to increase pressure from a stored source.
• Agricultural and Industrial Use: Supplying water for livestock, irrigation systems, or manufacturing processes where consistent water availability is vital.

The concept of cisterns is not new; ancient civilizations used them to manage water resources effectively. Modern technology has only improved their efficiency, durability, and accessibility for homeowners and businesses alike. Understanding the different types available today will help you pinpoint the perfect fit for your specific requirements.

Key Factors to Consider When Choosing a Cistern

Before diving into the types, let’s quickly cover what you should think about. These points will help you narrow down your choices:

• Capacity: How much water do you need to store? Consider usage patterns, rainfall amounts (if harvesting), and long-term goals.
• Material: Durability, cost, and potential impact on water quality are important.
• Installation Location: Above ground, below ground, or integrated? This depends on space, aesthetics, and frost protection needs.
• Budget: Costs vary significantly based on size, material, and installation complexity.
• Purpose: Is it for drinking water, irrigation, fire suppression, or general backup?
• Regulations: Check local building codes and health department regulations regarding water storage.
• Maintenance: Some materials or types require more upkeep than others.

Types of Cisterns Based on Material

The material of a cistern significantly impacts its lifespan, cost, durability, and suitability for different applications. Here’s a look at the most common materials:

1. Concrete Cisterns

Concrete cisterns have been a traditional choice for a long time. They are known for their robust construction and longevity, often lasting for decades. They can be poured on-site or pre-cast.

• Pros:
  • Extremely durable and can last 50-100 years or more.
  • Excellent thermal mass, keeping water cooler in summer and preventing freezing in winter (especially when buried).
  • Resistant to corrosion and UV damage.
  • Can be custom-built to specific sizes and shapes on-site.
  • Good for underground installations as they can withstand soil pressure.
• Cons:
  • Very heavy, requiring sturdy foundations or excavation.
  • Can be expensive to construct, especially on-site pours.
  • Porous material can allow contaminants to leach in if not properly sealed.
  • Can crack over time due to ground shifts or freeze-thaw cycles if not installed correctly.
  • May require a different type of lining or sealants to make them food-grade for potable water storage.

Concrete cisterns are a solid choice for underground storage where durability and longevity are paramount. For potable water, ensure that the concrete mix and any sealants used are certified as safe for drinking water. Organizations like the U.S. Environmental Protection Agency (EPA) offer guidelines on safe water storage practices.

2. Fiberglass Cisterns

Fiberglass (also known as glass-reinforced plastic or GRP) cisterns are a popular modern option. They are lightweight, strong, and resistant to corrosion.

• Pros:
  • Lightweight, making them easier to transport and install compared to concrete or steel.
  • Non-corrosive, making them ideal for areas with high salinity or moisture.
  • Smooth interior surface, reducing the risk of bacterial growth and making cleaning easier.
  • Generally good chemical resistance.
  • Can be manufactured in various sizes and shapes.
• Cons:
  • Can be more expensive than plastic cisterns initially.
  • Susceptible to damage from impact or abrasion during installation or by heavy ground loads if not properly backfilled.
  • Less resistant to UV radiation over very long periods, often requiring protection from direct sunlight if installed above ground.
  • May require professional installation to ensure proper support and anchoring.

Fiberglass cisterns are excellent for both above-ground and below-ground installations, offering a good balance of strength, weight, and resistance to degradation.

3. Metal Cisterns (Steel & Galvanized Steel)

Metal cisterns, particularly those made from galvanized steel, have been used for many years. They are strong and can hold large volumes of water.

• Pros:
  • Very strong and durable, able to withstand significant pressure.
  • Can be manufactured in large capacities.
  • Galvanized coating provides some rust resistance.
  • Relatively long lifespan if maintained properly.
• Cons:
  • Susceptible to rust and corrosion, especially at welds or if the coating is damaged, leading to leaks over time.
  • Galvanizing can sometimes leach zinc into the water, which may be a concern for potable use without proper treatment.
  • Heavy, requiring careful installation and often a solid foundation.
  • Can be prone to denting.
  • Temperature of the water can fluctuate more than in other materials.

For potable water, stainless steel is a better, though more expensive, option. Galvanized steel is more common for non-potable applications like agricultural water or fire suppression where slight mineral content isn’t an issue.

4. Plastic (Polyethylene/HDPE) Cisterns

Polyethylene (often HDPE – High-Density Polyethylene) cisterns are the most common choice for residential rainwater harvesting and backup water storage today. They are relatively affordable, lightweight, and available in many shapes and sizes.

• Pros:
  • Cost-effective and generally the most budget-friendly option.
  • Lightweight, making them extremely easy to transport and install.
  • Corrosion-resistant and won’t rust.
  • Available in opaque colors or treated for UV resistance, making them suitable for outdoor use.
  • Seamless construction (for many) means fewer leak points.
  • Generally safe for potable water storage if certified (e.g., NSF certified).
• Cons:
  • Can be susceptible to UV degradation if not properly treated or if stored improperly.
  • Less resistant to extreme temperatures or physical damage than concrete or metal.
  • May expand or contract more with temperature changes.
  • Smaller capacities are more common; very large capacity plastic tanks can be more prone to structural issues without significant support.
  • Can sometimes impart a slight “plastic” taste to water if not a high-quality, food-grade material.

These are excellent all-around choices for most rainwater harvesting and backup supply needs. Always look for food-grade or NSF-certified polyethylene tanks for storing water intended for consumption or household use. Reputable manufacturers will clearly state their product’s suitability for potable water. For instance, the Plastics Industry Association can offer insights into material standards.

Types of Cisterns Based on Installation & Design

Beyond material, how and where a cistern is installed also defines its type and function. This often dictates its footprint, capacity, and accessibility.

1. Above-Ground Cisterns

These are tanks that sit on the surface of the ground, on a prepared foundation or pad. They are typically visible and accessible.

• Pros:
  • Much easier and cheaper to install, as minimal excavation is required.
  • Easier to inspect, clean, and maintain.
  • Less risk of ground pressure causing damage.
  • Can be moved if necessary (especially lighter plastic or fiberglass models).
  • Faster installation time.
• Cons:
  • Can be an eyesore, taking up yard space.
  • More exposed to temperature fluctuations, which can affect water temperature and risk freezing in colder climates.
  • Must be anchored securely to prevent tipping, especially in high winds.
  • Less protection from UV damage (unless specifically treated) and physical impact.
  • Requires space above ground.

Above-ground cisterns are a practical choice for homeowners looking for a simple and cost-effective water storage solution, particularly in milder climates or for non-potable uses like garden irrigation.

2. Below-Ground (Underground) Cisterns

These are tanks installed in a hole dug in the ground, typically covered with earth. They are often preferred for aesthetic reasons and protection.

• Pros:
  • Aesthetically pleasing as they are completely hidden.
  • Water temperature is more stable, protected from extreme highs and lows, and less prone to freezing.
  • Protected from UV damage and physical impact.
  • Can often accommodate larger capacities in a smaller surface footprint.
  • Can be installed under driveways or other paved areas with appropriate structural design.
• Cons:
  • More complex, time-consuming, and expensive to install due to excavation and structural considerations.
  • More difficult to inspect, clean, and maintain; repairs can be costly.
  • Requires careful consideration of soil type, water table, and potential ground movement.
  • Lighter cisterns (like plastic) require robust anchoring and careful backfilling to prevent collapse from external soil pressure.
  • Access points must be securely covered, often with traffic-rated lids if installed under driveways.

Below-ground cisterns are ideal when aesthetics are a priority, space is limited above ground, or when protection from freezing is a major concern. Materials like concrete, fiberglass, and specially reinforced plastic tanks are commonly used for this purpose.

3. Modular Cisterns

These are multi-piece or interlocking tanks that can be assembled on-site to create a custom-sized storage system. They are particularly useful when access to the installation site is difficult, as individual modules can be carried or maneuvered into place.

• Pros:
  • Flexible sizing – can be expanded or reconfigured.
  • Easier to transport and install in locations with restricted access.
  • Can often be assembled to fit awkward spaces.
• Cons:
  • The seams between modules can be potential points of leakage if not sealed meticulously.
  • Installation can still be complex depending on the system.
  • May be more expensive per gallon than large, single-piece tanks.

Modular cisterns are a smart solution for challenging installations where standard large tanks would be impractical.

4. Freestanding Cisterns

This term often refers to above-ground tanks that are designed to stand on their own without being buried. They come in various shapes—cylindrical, rectangular, or even decorative—and are usually made of plastic, fiberglass, or metal.

• Pros:
  • Simple installation.
  • Easy access for maintenance.
  • Can be aesthetically integrated into landscaping or chosen for their design.
• Cons:
  • Take up visible space.
  • More susceptible to temperature extremes and UV damage.
  • Require solid anchoring.

5. Bathtub Cisterns (Very Large Scale / Industrial)

While not a common residential term, very large, low-profile, wide tanks are sometimes colloquially referred to by analogy to bathtubs due to their shape. These are typically large plastic or fiberglass tanks designed for substantial water storage, often for agricultural, commercial, or industrial use, and are usually installed above or partially below ground.

• Pros:
  • High capacity.
  • Low profile can make them easier to site in some situations.
  • Efficient use of space for volume.
• Cons:
  • Require significant space due to width.
  • Installation can still be challenging due to size and weight.
  • Need robust structural support.

Cisterns for Rainwater Harvesting vs. Backup Water Storage

While many cistern types can serve dual purposes, there are some considerations specific to their primary use.

Rainwater Harvesting Cisterns

For rainwater harvesting, the key is capturing and storing water efficiently. This often means connecting to your roof’s gutter system. Important features include:

• First Flush Diverter: This is a crucial accessory that diverts the initial, dirtiest runoff from the roof away from the tank.
• Leaf Screens/Gutter Guards: To prevent debris from entering the cistern.
• Tank Material: Food-grade plastic or fiberglass are excellent to maintain water purity without chemical leaching.
• Opaque or UV-Treated: To prevent algae growth inside the tank.

Many homeowners opt for above-ground plastic cisterns due to ease of installation and cost-effectiveness for garden use, or below-ground tanks for a cleaner aesthetic and better temperature regulation.

Backup Water Storage Cisterns

For emergency backup, ensuring the water remains potable and accessible when needed is paramount. This might involve:

• Potable Water Certification: Ensuring the tank material and any internal components are certified safe for drinking water (e.g., NSF/ANSI 61).
• Protection from Contamination: Secure lids and proper venting are essential.
• Reliable Delivery: A good quality pump, pressure tank, and filtration system are often integrated.
• Protection from Freezing: Below-ground installation or adequate insulation is vital in colder climates.

For backup potable water, underground concrete or high-quality, food-grade fiberglass or plastic tanks are often preferred for their durability and stable temperatures.

Cistern Installation: What You Need to Know

While the specifics of installation vary greatly depending on the cistern type, material, and location (above/below ground).