As an affiliate, we may earn a commission from qualifying purchases. We get commissions for purchases made through links on this website from Amazon and other third parties.
Cisterns can store much more rainwater than a typical rain barrel, but they also bring more cost, space, plumbing, and maintenance needs. Large cisterns can be heavy when full, harder to clean, and more difficult to repair or replace. Underground cisterns add excavation and access concerns, while above-ground tanks need a stable base and protection from weather.
For many rainwater systems, the biggest disadvantages are not the tank itself. They come from installing a cistern that is too large, poorly placed, hard to access, or not matched to the way the water will be used.
The Main Disadvantages of Cisterns
The most common drawbacks include:
- Higher installation cost than simple rain barrels
- Large space requirements
- Very heavy loads when full
- More plumbing and overflow planning
- Ongoing cleaning and inspection
- Pumping requirements in some systems
- Risk of algae, sediment, insects, or contamination if poorly managed
- Difficult repairs or replacement
- Freeze concerns in cold climates
- More complicated installation for underground tanks
These disadvantages matter differently depending on the cistern's size, location, and intended use.
Cisterns Can Take Up a Lot of Space
A large cistern needs a large footprint.
This can be a problem on a small property where space is already needed for walkways, gardens, parking, utilities, or drainage.
The tank also needs room around it for:
- Pipe connections
- Inspection
- Cleaning
- Pump service
- Overflow drainage
- Future repairs
Placing a tank tightly between buildings or fences may save space at first, but it can make maintenance much harder later.
Before choosing a cistern, check its actual outside dimensions rather than looking only at its gallon capacity.
A Full Cistern Is Extremely Heavy
Water weighs about 8.3 pounds per U.S. gallon.
That means even a modest cistern can become very heavy when full. The tank itself adds more weight.
For example, the water inside a 1,000-gallon cistern weighs more than 8,000 pounds.
This is why a cistern cannot simply be placed wherever it fits. Above-ground tanks generally need a firm, level, properly prepared base that can support the full load without settling or shifting.
Decks, elevated platforms, roofs, and other structures require special caution. Do not assume an existing structure can safely carry a filled cistern. A qualified professional may be needed to assess structural loads.
Installation Is More Complicated Than Using Rain Barrels
A basic rain barrel may only require a downspout connection and overflow hose. A cistern usually needs more planning.
A complete system may include:
- Gutters and downspouts
- Leaf screens
- A first-flush device
- An inlet
- An overflow
- Tank vents
- An outlet
- Valves
- A pump
- Filters
- Electrical controls
A first-flush device diverts some of the first roof runoff from a storm. This water often carries more dust, leaves, bird droppings, and other debris from the roof.
Each additional part creates another connection that must fit correctly and remain accessible.
Poorly planned plumbing can cause leaks, slow filling, blocked pipes, overflowing, or difficulty draining the tank.
Large Cisterns Need Good Overflow Planning
A cistern will eventually fill during enough rainfall.
Once it is full, every additional gallon entering the tank must go somewhere.
An undersized or badly placed overflow can send water toward:
- Building foundations
- Crawl spaces
- Walkways
- Neighboring property
- Erosion-prone soil
A rainwater system should therefore include an overflow path capable of safely carrying excess water away from structures.
The overflow should also be protected against insects and debris without restricting water flow.
Sediment Builds Up Over Time
Roof runoff carries small particles even when gutters and inlet screens are used.
Some of this material settles at the bottom of the cistern. Over time, sediment can become deep enough to affect water quality or reach the tank outlet.
Good prefiltration helps reduce buildup, but it does not eliminate maintenance.
A cistern should be installed so that inspection and cleaning are possible. A tank that cannot be reached or drained conveniently may become much harder to maintain.
Do not enter a cistern to clean it. Tanks and other enclosed spaces can create serious confined-space hazards.
Poor Maintenance Can Cause Water-Quality Problems
Stored rainwater is not automatically clean or safe.
Leaves, dust, animal waste, insects, organic matter, and roof contaminants can enter the system. Warm conditions and sunlight can also encourage biological growth.
A well-designed cistern can reduce these problems through features such as:
- Covered storage
- Light-blocking tank walls
- Screened openings
- Roof debris control
- First-flush diversion
- Proper overflow screening
- Regular inspection and cleaning
The level of treatment needed depends on how the water will be used.
Water used for garden irrigation does not normally require the same treatment approach as water intended for household use.
Water intended for drinking requires much more careful system design. Collection, prefiltration, treatment, current laboratory testing, maintenance, and applicable local requirements all matter. A single filter or treatment device should not be treated as proof that collected rainwater is potable.
Potable means suitable for drinking. Non-potable water is water not intended for drinking.
Pumps May Be Needed
Gravity works well when the tank is high enough above the point where water is used. Large cisterns, however, are often installed at ground level or underground.
In those systems, a pump may be needed to supply usable flow and pressure.
Adding a pump brings several disadvantages:
- Electricity may be required.
- The pump adds maintenance.
- Dry running can damage some pumps.
- Filters can reduce available flow.
- Pressure controls may be needed.
- Pumps and pipes may need freeze protection.
Pump selection must also match the job.
The required flow rate is how much water must move during a certain amount of time. Head height describes how much vertical lift and resistance the pump must overcome.
A pump that works for filling a watering can may not provide enough flow or pressure for several irrigation zones or household fixtures.
Underground Cisterns Are Harder to Install
An underground tank saves surface space and can help protect stored water from sunlight. However, installation is much more involved.
Excavation can encounter:
- Buried utilities
- Rock
- Groundwater
- Unstable soil
- Poor drainage
The tank must also be designed for underground installation. A tank intended only for above-ground use should not be buried unless its manufacturer specifically permits it.
Underground tanks may also need careful planning for access, backfilling, groundwater conditions, and vehicle loads.
Excavation and entry into pits can be dangerous. Large or deep installations are often better handled with professional help.
Repairs Can Be Difficult
Review choosing a cistern instead of a well to evaluate tank venting and overflow control during extended storage.
A small rain barrel can often be emptied, moved, or replaced fairly easily.
A large cistern may be permanently connected to several pipes and surrounded by landscaping, fencing, soil, or equipment.
Problems such as a damaged fitting or leaking connection may require:
- Draining hundreds or thousands of gallons
- Removing plumbing
- Excavating around a buried tank
- Moving equipment for access
A bulkhead fitting is a fitting that passes through the tank wall and creates a sealed pipe connection. These fittings are common at outlets and other connections.
Installing them where they cannot be reached later can turn a small repair into a large project.
Cisterns Can Freeze in Cold Climates
Freezing weather creates another challenge.
Water expanding as it freezes can damage pipes, valves, pumps, and fittings. Exposed plumbing is often more vulnerable than the large body of water inside the tank.
Cold-climate systems may require seasonal draining, protected plumbing, buried lines, insulation, or other freeze-control measures appropriate for the local climate.
No freeze-protection method should be assumed to guarantee that a system cannot freeze.
Mosquitoes Can Become a Problem
Any opening that allows mosquitoes into stored water can create a breeding area.
Inlets, vents, overflow pipes, access openings, and damaged screens are common points that deserve attention.
Tightly fitting covers and suitable screens help reduce the risk. They still need regular inspection because screens can tear, loosen, or become blocked.
Avoid leaving openings uncovered simply because the cistern itself has a lid.
Stored Water Can Develop Algae
Algae usually becomes more likely when sunlight reaches stored water.
Clear or translucent tanks can therefore be more troublesome when installed outdoors in direct light.
An opaque cistern that blocks sunlight generally makes algae control easier. Covered openings and good debris control also help.
If algae keeps returning, simply adding a chemical without understanding the cause is not a good long-term solution, especially when the water has household uses.
Water Can Sit Too Long
A very large cistern is not always better.
If storage capacity is much greater than normal water use, some water may remain in the tank for long periods.
That can increase maintenance concerns, especially when organic material is entering the tank.
Cistern size should therefore be based on both supply and demand.
Important factors include:
- Roof collection area
- Local rainfall patterns
- Intended water use
- Expected dry periods
- Available space
- Overflow capacity
A bigger tank provides more storage, but unused capacity does not automatically make a system better.
Cisterns Do Not Guarantee a Continuous Water Supply
A cistern can only store water that has already been collected.
Long dry periods can empty even a large tank. A small roof may also collect less water than expected, even when storage capacity is high.
Rainwater availability depends on roof area, rainfall, collection losses, and water use.
This makes a cistern different from a conventional water supply. Users should not assume that installing a large tank guarantees water will always be available.
More Equipment Means More Maintenance
A larger rainwater system often contains more parts than a simple barrel setup.
Depending on the design, maintenance may include checking:
- Gutters
- Leaf screens
- First-flush devices
- Inlet filters
- Tank screens
- Sediment
- Pumps
- Valves
- Overflow pipes
- Treatment equipment
Ignoring one part can affect the rest of the system.
For example, a clogged inlet filter can reduce collection. A blocked overflow can cause flooding. A neglected pump intake can reduce water flow.
Easy access to these parts is therefore an important part of good cistern design.
When a Cistern May Not Be the Best Choice
A large cistern may not make sense when:
- Only a small amount of garden water is needed.
- There is little room for a tank.
- The property has no suitable tank base.
- Excavation would be difficult.
- The roof collection area is very small.
- Maintenance access would be poor.
- A simpler rain barrel system can meet the same goal.
For small garden needs, one or more rain barrels may be easier to install and maintain.
For larger irrigation systems, cabins, household reuse, or properties with long dry periods, the added capacity of a cistern can justify the extra complexity.
The better choice is the one that matches how much water you can collect, how much you plan to use, and how much maintenance you can reasonably handle.
Frequently Asked Questions
What is the biggest disadvantage of a cistern?
For many homeowners, the biggest disadvantage is the added complexity. A large cistern needs a suitable base or excavation, proper plumbing, safe overflow routing, maintenance access, and sometimes a pump.
Are cisterns expensive to maintain?
Maintenance needs vary by system. A simple irrigation cistern may mainly require cleaning screens, checking fittings, and managing sediment. Systems with pumps, filters, controls, or treatment equipment require more upkeep.
Can a cistern damage a foundation?
Poor placement or overflow routing can send water toward a foundation. The cistern's own weight can also affect unsuitable surfaces. The tank should have a stable base, and overflow water should be directed safely away from structures.
Do cisterns get algae?
They can. Algae is more likely when sunlight reaches stored water and nutrients are present. Opaque tanks, covered openings, debris control, and regular maintenance can reduce the conditions that encourage algae.
Do cisterns attract mosquitoes?
They can if mosquitoes can reach the water. Inlets, vents, access openings, and overflow pipes should be properly protected with suitable screens or covers and inspected regularly.
Can you drink water directly from a rainwater cistern?
Do not assume cistern water is safe to drink. Roof runoff can contain biological and chemical contaminants. Drinking-water use requires appropriate collection, treatment, current laboratory testing, regular maintenance, and compliance with applicable local requirements.
Is an underground cistern better than an above-ground cistern?
Neither is always better. Underground cisterns save surface space and block sunlight well, but excavation, access, groundwater, and installation are more complicated. Above-ground tanks are easier to inspect and service but take up visible space and may need more protection from weather and freezing.
