A cistern is a sealed tank that stores water, often rainwater, for later household, garden, or emergency use.
Cisterns keep water on hand when you need it. Town supply shuts off, wells run low, gardens dry out. A well-built tank bridges those gaps. It pairs with a roof or another source, holds the water safely, and feeds taps, hoses, or appliances through simple plumbing.
What Exactly Is A Water Cistern System?
A cistern is a purpose-built container that keeps water clean and ready for later use. Many homes channel rain from the roof into a covered tank. Others truck in potable water and store it. Unlike a well that draws from the ground, a cistern relies on a waterproof shell and tight lids, screens, and overflows to keep debris and pests out.
You will see cisterns made from concrete, polyethylene, fiberglass, steel, or block with a lining. Some sit above grade where you can see and service them. Others hide below a patio or driveway to save space and control temperature swings. Capacity ranges from small barrels to large buried tanks that serve an entire house.
Cistern Types And Typical Uses
| Type | Where It Sits | Common Uses |
|---|---|---|
| Aboveground tank | Yard or basement | Garden hoses, toilet flush, laundry with treatment |
| Underground tank | Buried near house | Whole-home supply, sprinkler reserve |
| Modular barrels | Linked beside downspouts | Planter watering, small tool wash |
| Bladder tank | Crawlspace or garage | Space-saving storage, seasonal backup |
| Roof-level header | Loft or roof deck | Gravity feed to fixtures with flow control |
| Fire reserve cistern | Street or yard | Draft point for firefighting crews |
How A Cistern Works
Think of the system in five parts: catchment, conveyance, storage, treatment, and distribution. Each part does a simple job so the water you store stays clearer and easier to use.
Catchment
Most homes use the roof. Clean roof surfaces shed water into gutters. Leaf screens block big debris at the start. A smooth, washable surface at the inlet helps reduce fine grit.
Conveyance
Downspouts route water to the tank. A first-flush diverter can shunt the dirty opening run to waste. Tight lids, screened vents, and mosquito-proof overflows keep the tank sealed while air can still move.
Storage
The tank takes in water through a calming inlet that slows the flow and limits sediment stir-up. A floating pickup or outlet raised above the floor sends the clearest layer onward. An overflow protects the tank during big storms and vents to a drain or safe area.
Treatment
Screening and good housekeeping go a long way. For uses that touch people or food, add fine filtration and disinfection. Common choices include cartridge filters, UV lamps, and chlorine contact time.
Distribution
A small pump and pressure tank deliver steady flow. Backflow prevention and clear labels separate nonpotable lines from drinking lines. Gravity setups can work where the tank sits higher than the fixtures.
What Is A Cistern Tank Used For At Home?
Nonpotable uses are the easiest wins: garden hoses, drip lines, toilet tanks, and some washers. These tasks do not need drinking-grade water, which keeps the setup simple and low risk.
Drinking use raises the bar. Roof runoff can carry germs, dust, smoke residues, and metals from fittings. Safe service needs proven filters, disinfectants, food-grade materials, and routine testing. Local rules may limit indoor uses without a permit or special gear. When in doubt, keep the cistern on nonpotable duty and save bottled or treated tap water for the glass.
Many rural homes store trucked-in water for whole-house use. Others hold a reserve for wildfire season. Some towns keep buried fire cisterns at the corner so crews can draft water when hydrants fail.
For safe setup and upkeep, see the CDC guidance on rainwater, the EPA Soak Up the Rain program, and the Texas Manual.
Materials, Shapes, And Siting
Tank Materials
Concrete offers mass and low light entry, which helps water stay cool and dark. It needs food-grade liners or coatings for drinking use. Joints and penetrations must be tight.
Polyethylene tanks are light, easy to place, and come in many sizes. Look for resin rated for potable water if people will drink it. Shield the tank from sun to extend life.
Fiberglass works well for buried or abovegrade installs. It resists corrosion and cleans easily. Spec a gel coat suited to the liquid you plan to store.
Steel tanks, often with a liner, offer large volumes and strong walls. Protect edges from rust, watch fasteners, and keep the liner in top shape.
Above Or Below Ground
Aboveground tanks cost less to place and are simple to inspect. They do see heat and light and may need insulation or shade. Underground tanks save yard space and hold stable temperatures, but excavation, bedding, and access hatches add work.
Form Factor
Round tanks tune pressure well and are common. Slimline tanks hug walls along a side path. Bladders slip under decks. Choose a shape that fits service paths for cleaning, valve access, and future pump swaps.
Sizing And Capacity
Right sizing keeps water turning over while still meeting demand. Three inputs drive the choice: roof area, local rainfall, and daily needs.
Estimate Supply
Start with roof plan area. Multiply by average rainfall and a collection factor near 0.8 to account for losses. The result suggests how many liters or gallons you can catch in a season.
Estimate Demand
List fixtures that will run on the cistern. Toilets, hose taps, a washer, or the whole house with treatment. Add daily volumes and any peak run needs, like sprinkler cycles or a multi-shower morning.
Balance Turnover
Pick a size that can ride through a dry spell without sitting full for months. Stale water invites taste issues and biofilm. A float switch that holds a small reserve and a top-up valve from a backup source can smooth the ride.
Water Quality And Safety
Keep light out and lids tight. Shade slows algae. Screens stop leaves and pests. Gutter cleaning cuts nutrient loads. These simple steps help every system, small or large.
For any use that touches people or food, run a fine filter and a trusted disinfectant. UV units work well on clear water. Chlorine needs the right dose and contact time. Replace cartridges on schedule and watch pressure drop as a cue.
Separate lines that feed toilets or hoses from lines that feed sinks. Label valves and hose bibbs. Add backflow devices where code calls for them. Cross-connections lead to real risk.
Storms and floods can change what sits on the roof and what seeps near the tank. After heavy weather, check clarity, odor, and test as needed. When in doubt, bypass the system until you clean and disinfect.
Maintenance That Keeps Water Clean
Simple routines prevent most headaches. Set reminders, keep a small kit of filters and sanitizer, and log what you do. The table lists common tasks and a handy pace.
| Task | Why It Matters | Typical Interval |
|---|---|---|
| Clean gutters and screens | Reduce leaves, grit, and nutrients | Seasonal or after storms |
| Flush first-flush device | Clear settled dirt from the opening run | Monthly in rainy seasons |
| Inspect lids, vents, overflow | Block pests and light; keep flow safe | Quarterly |
| Swap filter cartridges | Maintain flow and particle removal | Per pressure gauge or schedule |
| Sanitize tank surfaces | Control biofilm and odors | Annually or after floods |
| Test water when used for people | Verify treatment and safety | Per local guidance |
Permits, Codes, And Labels
Many areas welcome rain storage for outdoor use. Indoor uses and drinking supply often need a permit, approved materials, and inspection. Look for rules on backflow protection, overflow routing, tank anchoring, and trench depths for buried lines.
Mark nonpotable outlets with clear words or a purple cap. Keep a simple diagram of valves and pipes near the tank. If a contractor or inspector visits, that map speeds the check and future service.
Cistern Versus Well And Septic
A well taps groundwater through a casing and pump. A cistern stores water you supply from rain, delivery trucks, or a spring. A septic tank treats wastewater and never belongs in a supply chain. Mixing supply and waste systems is unsafe and illegal in many places.
Old homes sometimes have a buried brick or stone cistern no longer in service. If you find one, seal it or rehab it with a liner and safe covers. Never leave an open void that can collapse or collect dirty water.
Buying, Installing, And Living With A Cistern
Plan
List the uses you want and note where the tank can sit. Measure roof area and downspout paths. Sketch pipe runs and a service pad for pumps and filters.
Choose Components
Pick a tank sized for your supply and demand. Add leaf guards, a first-flush unit, a calming inlet, a floating pickup, a pump, a pressure tank, filters, and a UV unit if needed. Select valves with clear labeling and union joints for easy swaps.
Install
Level the base, anchor per the tank maker, and route pipes with smooth sweeps. Seal penetrations. Keep sun off plastic where you can. For buried tanks, use proper bedding and add risers for hatch access.
Commission
Rinse the tank, run water through filters, and check every joint for leaks. Label lines and photograph the setup. Start a log for filter changes and sanitation dates.
Live With It
Watch pump cycles, listen for odd sounds, and track how the water turns over across seasons. Small tweaks like shade cloth, a bigger prefilter, or a timer on a hose tap can save water and extend gear life.
Who Uses Cisterns Today?
Homes on small islands. Cabins off the grid. City lots with low pressure. Suburbs that want greener yards. Farms that value every drop. Schools that teach kids where water comes from. Across all of those places, a cistern brings resilience and saves treated tap water for tasks that truly need it.
Builders and plumbers like cisterns for another reason: they are modular. Start with a barrel bank for plants. Grow into a buried tank later. The same downspouts, screens, and pumps can scale with you.
Quick Glossary
Key Terms
- First-flush diverter: A device that diverts the initial dirty runoff from a storm.
- Calming inlet: A diffuser that slows incoming water to protect the clear layer.
- Floating pickup: An intake that draws from just below the surface.
- Backflow preventer: A valve that stops water from reversing into clean lines.
- Nonpotable: Water not intended for drinking or cooking.
The Bottom Line On Cisterns
A cistern is simple gear that pays off in steady service. Pick the right size, keep light and pests out, filter for the job, and follow a small maintenance routine. Do that and your tank will serve for years with clear, useful water on tap.
Common Mistakes And Easy Fixes
Oversizing the tank so water sits for months leads to flat taste. Match volume to real demand and design for steady turnover. A float valve or controlled top-up keeps water moving.
Skipping pre-screens and a first-flush unit loads the tank with grit. Fit both near gutters and clean on a schedule. The tank stays cleaner and filters last longer.
Clear plastic tanks look neat, then grow algae under sun. Opaque walls or a wrap solve that. Shade and insulation protect pumps from heat.
Mixing potable and nonpotable lines without labels risks cross-flow. Use separate piping, purple-coded parts, and backflow devices where rules clearly call for them.
Leaving the overflow to dump on soil can erode footings and invite pests. Pipe it to a drain, a soakaway, or a safe swale with screens on the end.
Not all roofs suit drinking use. Old lead paint, certain soft woods, and asphalt dust can add unwanted material to runoff. When you plan to drink the water, pick roof finishes and gutters rated for that duty and add treatment that fits the risk profile.