8 Supplies for Installing a Large Rainwater Harvesting Tank

Watching a summer storm dump hundreds of gallons of water off your barn roof only to watch it disappear into the mud is a frustrating sight for any hobby farmer. Installing a large-scale rainwater harvesting system turns that wasted runoff into a reliable, free resource for your crops and livestock during dry spells. Achieving this requires more than just placing a barrel under a downspout; it demands a coordinated system of heavy-duty components designed to keep your water clean, secure, and easily accessible.

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Planning Your Large Rainwater Harvesting System

Capturing rainwater at a scale that actually sustains a small farm requires calculating your roof runoff potential and matching it with your dry-season water needs. A single heavy downpour can generate thousands of gallons of water from a modest barn or workshop roof. Without proper planning, you will either undersize your storage or end up with a chaotic, overflowing mess near your foundation.

Location is everything when setting up a massive storage footprint. The tank must sit close enough to your collection roof to minimize complex pipe runs, yet remain accessible for gravity-fed distribution or pump hookups. You also need to account for the weight of the water, as a fully loaded thousand-gallon tank weighs over four tons and will sink into unprepared soil.

Before purchasing a single fitting, map out the entire flow of water from the shingles to the garden bed. This means identifying where the diverters will sit, how the overflow will be routed away from structures, and where power will be sourced if you plan to use an electric pump. Taking the time to sketch these connections prevents costly mid-installation trips to the hardware store.

Storage Tank – Norwesco 1050 Gallon Vertical Tank

The storage tank is the anchor of your entire harvesting setup, holding the bulk of your water reserve for when dry spells hit. A flimsy container will bow, crack under UV exposure, or contaminate your water supply with algae within a single season. You need a heavy-duty, food-grade vessel that can withstand the elements while holding enough volume to make a difference on a small farm.

The Norwesco 1050 Gallon Vertical Tank is the industry standard for small-scale agricultural water storage. Molded from rugged, high-density polyethylene, this tank features a seamless construction that eliminates weak points prone to splitting. Its dark green or black color blocks sunlight completely, preventing the photosynthesis that fuels algae growth inside the tank.

• Dimensions: 81-inch diameter by 57-inch height, requiring a wide, level footprint.
• Inlet/Outlet: Comes with a standard 2-inch top fill opening and a 2-inch bottom drain.
• Weight: Weighs approximately 185 pounds empty, requiring at least two people to maneuver into place.

Because of its size, delivery access to your property must be clear of low-hanging branches and tight gates. This tank is perfect for growers with moderate-to-large garden plots or small livestock herds who need a dependable, long-term water reserve. It is not suitable for those with limited yard space or those looking for a portable, temporary water storage solution.

Downspout Diverter – Oatey Mystic Collection System

Standard downspouts dump water indiscriminately, but a downspout diverter channels that flow directly into your storage system. It acts as the gateway, redirecting clean roof runoff while allowing heavy debris to continue down the main gutter channel. Without one, you are left with the headache of manually routing rigid PVC pipes directly into the top of your tank.

The Oatey Mystic Collection System simplifies this connection by fitting directly into standard 2×3-inch residential downspouts. Constructed from durable, UV-resistant plastic, this diverter uses a unique internal design that captures water flowing along the outer walls of the downspout while letting leaves pass through the center. It includes a high-quality flexible hose that stretches to connect directly to your tank inlet.

• Compatibility: Designed specifically for 2×3-inch metal or vinyl downspouts.
• Installation: Requires cutting a small section out of your existing downspout, making a hacksaw and tape measure essential tools.
• Maintenance: The internal channel can occasionally clog with pine needles or small twigs, requiring a quick seasonal flush.

This diverter is ideal for hobby farmers utilizing standard residential-sized gutters on sheds, garages, or small barns. It is not designed for heavy commercial gutter systems or high-volume downspouts draining massive metal barn roofs.

First Flush Diverter – Blue Mountain First Flush Kit

The first few minutes of any rainfall wash away accumulated bird droppings, dust, pollen, and debris from your roof. A first flush diverter captures this initial, highly contaminated water and isolates it before it can enter your main storage tank. Skipping this step guarantees a layer of foul-smelling sludge will build up at the bottom of your tank, ruining water quality.

The Blue Mountain First Flush Kit is an exceptionally reliable gravity-fed system that uses a simple, elegant design to protect your water. As the rain begins, the dirtiest water enters the diversion chamber, lifting an internal ball float that seals off the chamber once full, allowing only clean water to flow into your tank. It features a slow-release drain valve that slowly empties the dirty water over time, resetting the system automatically for the next storm.

• Pipe Requirements: Requires a length of standard 3-inch or 4-inch PVC pipe (not included) to act as the diversion chamber.
• Sizing: You must calculate the chamber length based on your roof surface area to ensure enough initial runoff is captured.
• Winterization: The bottom drain must be kept clear and unscrewed before freezing temperatures hit to prevent ice from splitting the PVC chamber.

This kit is a must-have for anyone planning to use harvested rainwater for overhead irrigation, livestock watering, or washing equipment. It is less critical for basic gravity-fed orchard watering where sediment build-up is not a concern for drip emitters.

Tank Screen – Blue Mountain Co Light Guard Screen

Even with a first flush diverter, wind-blown debris, mosquitoes, and pests can find their way into your tank’s main inlet. A high-quality tank screen acts as a physical barrier at the entry point of your tank, keeping out leaves while preventing pests from breeding in your water supply. It is your last line of defense for maintaining pristine water quality inside the reservoir.

The Blue Mountain Co Light Guard Screen stands out because it combines an ultra-fine mesh screen with a light-blocking cover. The integrated light guard blocks sunlight from entering the top of the tank, which drastically reduces algae growth at the water’s surface. Its stainless steel mesh is fine enough to keep out even the smallest mosquitoes while maintaining a high flow rate during heavy downpours.

• Size Options: Available in multiple diameters, so you must measure your tank’s top opening precisely before ordering.
• Maintenance: Leaves can pile up on top of the screen, requiring a quick brush-off after major windstorms.
• Fit: May require securing with screws into the polyethylene tank lip to prevent strong winds from blowing it away.

This screen is essential for farmers in mosquito-prone areas or those with tanks positioned under overhanging trees. It is not necessary if your tank is completely sealed and fed exclusively through a closed, pressurized pipe system.

Bulkhead Fitting – Banjo Double Threaded Fitting

Getting water into a tank is easy, but getting it out without leaks requires a heavy-duty connection through the tank wall. A bulkhead fitting creates a watertight seal around a hole drilled into the polyethylene, allowing you to attach valves, hoses, or pumps. A cheap, flimsy fitting will eventually weep water, slowly draining your hard-earned supply into the soil.

The Banjo Double Threaded Fitting is the gold standard for agricultural liquid handling. Made from glass-reinforced polypropylene, it offers incredible strength, chemical resistance, and UV stability. It features heavy-duty EPDM gaskets that compress tightly against the curved wall of the tank, ensuring a permanent, leak-free seal even under the pressure of a thousand gallons of water.

• Thread Type: Features female NPT threads on both sides, allowing you to screw pipes into both the inside and outside of the tank.
• Installation: Requires drilling a precise hole using a hole saw; a reverse-thread locknut ensures the fitting does not loosen when you screw in valves.
• Gasket Placement: The gasket must always be placed on the flange side inside the tank to seal correctly.

This fitting is perfect for anyone installing high-flow valves or connecting rigid PVC pipe to their tank. It is not suitable for thin-walled barrels that cannot handle the compression force of a professional-grade bulkhead.

Utility Pump – Wayne PC4 Cast Iron Transfer Pump

Gravity feed is fine for a nearby garden bed, but moving water uphill or running a sprinkler system requires mechanical pressure. A utility pump draws water from the bottom of your tank and pressurizes it, giving you the power to run long hose runs or overhead watering systems. Without a pump, your large-scale rainwater system is limited to low-pressure drip lines and watering cans.

The Wayne PC4 Cast Iron Transfer Pump is a rugged, high-performance pump designed for heavy farm use. Powered by a 1/2 horsepower motor, it can pump up to 1,450 gallons per hour, easily generating the pressure needed for multiple garden hoses. Its durable cast iron housing shrugs off the bumps and drops of outdoor farm life, while the included brass garden hose adapters make hookups incredibly simple.

• Power Source: Requires a standard 120V electrical outlet nearby or a heavy-duty extension cord.
• Priming: This is a non-submersible pump that must be manually primed with water before every use to avoid damaging the internal impeller.
• Suction Hose: Requires a reinforced suction hose on the inlet side to prevent the hose from collapsing under vacuum pressure.

This pump is ideal for growers who need to move water over long distances, up steep slopes, or run high-pressure sprinklers. It is not suitable for those looking for a silent, automated system that turns on and off automatically with a faucet squeeze.

Tank Gauge – Rain Harvesting Mirus Level Indicator

Operating a large rainwater system blindly is a recipe for running your pump dry or running out of water right when your crops need it most. A reliable tank gauge lets you monitor your water reserves at a glance without having to climb a ladder to peer inside. It provides the crucial data you need to budget your water use during dry spells.

The Rain Harvesting Mirus Level Indicator is a clever, non-electric gauge that uses a simple weighted float and counterweight system. As the water level rises or falls, the highly visible indicator on the outside of the tank moves accordingly, showing the exact level from a distance. Because it requires no batteries or electrical wiring, it is completely weatherproof and exceptionally reliable in remote farm settings.

• Installation: Requires drilling a small hole in the top dome of the tank to route the internal guide strings and float.
• Calibration: You must adjust the string length during installation to match the exact height of your specific tank.
• Clearance: The indicator moves along the outside wall of the tank, so you must keep this area free of climbing vines or stored equipment.

This gauge is perfect for off-grid setups and busy farmers who want a simple, visual way to monitor water levels from across the yard. It is not necessary for small, translucent tanks where the water line is easily visible through the plastic.

Overflow Outlet – Rain Harvesting Flanged Outlet

A thousand-gallon tank can fill surprisingly fast during a torrential downpour, and once full, that excess water has to go somewhere. An overflow outlet directs this high-volume surplus away from your tank’s foundation and your home’s structure. Without a designated, high-capacity overflow, water will spill out of the top screen, eroding the base of your tank and destabilizing the entire site.

The Rain Harvesting Flanged Outlet is designed specifically to handle high-volume overflow events with ease. Its wide, flanged design allows for a secure, leak-free connection to the upper wall of your tank using simple screws and sealant. The outlet features a built-in mosquito-proof screen, ensuring that while excess water can escape, pests cannot use the overflow pipe as an entry point into your clean water.

• Sizing: Must be matched to or exceed the size of your inlet pipe to prevent water from backing up in the tank.
• Routing: You will need to attach a length of flexible hose or rigid PVC to the outlet to carry the overflow to a safe drainage area or rain garden.
• Installation Height: Must be mounted as high as possible on the tank wall to maximize your total storage capacity.

This outlet is essential for any large-scale rainwater harvesting setup connected to a large roof footprint. It is not needed if your system utilizes a closed-loop diverter that automatically bypasses the tank once it reaches capacity.

Preparing a Solid Gravel Base for Your Tank

A thousand gallons of water weighs roughly 8,300 pounds. Placing that kind of concentrated weight on raw soil is a recipe for disaster, as the ground will unevenly settle, causing the tank to tilt, stress its fittings, and potentially crack. Preparing a flat, compacted, and well-drained foundation is the most critical step of the entire installation process.

Start by excavating the site to a depth of four to six inches, making the footprint at least one foot wider than the diameter of your tank. Frame the excavated area with pressure-treated timber or landscape timbers to contain the base material. Fill the framed area with a three-inch layer of crushed limestone or road base gravel, leveling it meticulously with a long straightedge and a spirit level.

Compact the gravel thoroughly using a hand tamper or a rented plate compactor until it is rock-hard and perfectly level. Top the compacted base with a thin, one-inch layer of pea gravel or coarse sand to cushion the bottom of the polyethylene tank and prevent sharp rocks from puncturing the plastic. Regularly check the level during this final step, as even a minor slope will become highly pronounced once the tank is filled.

How to Connect Your Tank to Garden Irrigation

Connecting your harvested rainwater to your garden irrigation system requires matching your water pressure to your watering method. If you are running a low-pressure drip irrigation system, gravity feed may suffice if your garden sits downhill from the tank. For drip systems, you will need to install a low-pressure backflow preventer, a 200-mesh filter to prevent sediment from clogging emitters, and a pressure regulator if using a pump.

For standard overhead sprinklers or hand-watering with a spray nozzle, you must integrate a utility pump into the system. Connect a short, flexible hose from the tank’s bottom bulkhead fitting to the pump’s inlet, ensuring all connections are sealed with Teflon tape to prevent air leaks. Run a heavy-duty garden hose from the pump outlet to your garden beds, using a manifold splitter if you want to run multiple lines simultaneously.

Always install a high-quality shut-off valve directly at the tank’s bulkhead fitting before connecting any hoses or pumps. This allows you to isolate the tank’s water supply for maintenance, pump repairs, or winterization without losing your stored water. Keep your irrigation lines elevated or buried shallowly to prevent tripping hazards and protect the hoses from UV degradation over the summer.

Essential Winter Maintenance for Large Tanks

Freezing water expands with immense force, capable of splitting heavy-duty polyethylene tanks, cracking brass valves, and ruining expensive pumps. If you live in an area with freezing winter temperatures, a proactive winterization routine is non-negotiable. Neglecting this chore can destroy your entire investment in a single cold snap.

Begin by draining the tank down to a safe level, or completely empty it if you expect prolonged deep freezes. Disconnect all external pumps, drain their internal chambers completely, and store them in a climate-controlled shed or basement. Open all bulkhead valves and leave them half-open; leaving a ball valve fully closed can trap water inside the ball mechanism, splitting the valve body when it freezes.

Disconnect your downspout diverter or switch it to "bypass" mode to prevent winter snowmelt and ice from entering the tank. Clean out all screens, first flush chambers, and gutters to prevent wet debris from freezing and warping the components. If you must keep water in the tank through winter, consider installing a floating stock tank de-icer or a bubbler system to keep the surface water moving and prevent solid ice formation.

Setting up a large-scale rainwater harvesting system is a highly rewarding weekend project that secures a vital resource for your hobby farm. By investing in rugged, high-quality components and preparing a solid foundation, you ensure your system will run smoothly for years to come. With your tank secured and winterized properly, you can face the dry summer months with the confidence of a self-reliant grower.