Ask any pressure washing operator what changed their business, and a surprising number will point to something that does not clean anything at all: the water tank. It sounds mundane, just a big container of water on a trailer, until you realize that most of the places you want to work, restaurants, storefronts, apartment complexes, do not have a spigot you can use. A water tank turns a machine that depends on someone else’s faucet into a self-contained rig that can work anywhere. It is the difference between taking the jobs you can reach and taking the jobs you want. If you are building or upgrading a rig, understanding the pressure washing water tank is essential.
This guide covers water tanks in full. We will explain what they do, why they matter, the types and materials, how to size one, how they integrate with the rig, plumbing and pumps, common setups, maintenance, and buying tips. By the end, you will know how to choose and use a water tank that makes your rig truly self-sufficient.
What a Water Tank Does
It stores water on your rig so you can work without connecting to a client’s water supply.
- Provides a water source anywhere you can park.
- Buffers demand between supply and the machine.
- Enables soft washing and chemical mixing.
- Makes the rig self-contained and more professional.
Without a tank, you are tethered to a hose bib. With one, you are free to work almost anywhere.
Why It Matters
- Access: Work at sites with no water.
- Professionalism: A self-contained rig looks and works like a real business.
- Independence: No waiting for a client to unlock a spigot.
- Consistency: Reliable water supply job after job.
- Flexibility: Combine with a pump to boost pressure and flow.
Types and Materials
| Material | Advantages | Notes |
|---|---|---|
| Polyethylene (poly) | Light, affordable, rust-proof, easy to fit | Most common for mobile rigs |
| Fiberglass | Strong, durable | Heavier, higher cost |
| Stainless steel | Very durable, professional | Heavy and expensive |
| Aluminum | Light, strong | Can react with some chemicals |
Poly tanks dominate mobile pressure washing for good reason: they are light, affordable, and handle the job.
Shapes and Configurations
- Horizontal tanks: Low profile, stable on trailers.
- Vertical or upright tanks: Tall and compact footprint.
- Flat or slim tanks: Fit tight spaces on trailers and trucks.
- Skid-mounted tanks: Built to sit on a skid with the machine.
- Baffled tanks: Reduce water sloshing during transport.
How to Size a Tank
Size depends on your machine’s flow, your typical job length, and refill access.
| Machine Flow (GPM) | Approx. Run Time per 100 Gallons |
|---|---|
| 1.5 GPM | Over an hour |
| 2.5 GPM | About 40 minutes |
| 4.0 GPM | About 25 minutes |
| 5.5 GPM | Under 20 minutes |
The math is simple: divide tank gallons by GPM to estimate run time. A larger tank means longer jobs without refilling, but more weight to tow.
Integrating the Tank with the Rig
- Mount securely to the trailer or skid with straps and brackets.
- Position for balance over the axles.
- Add a shutoff valve and outlet fittings.
- Plumb to the machine, using a transfer pump if gravity flow is insufficient.
- Include a filter to protect the pump.
- Provide a fill point and overflow.
- Baffle or manage water movement.
Plumbing and Pumps
- Gravity feed: Tank above the machine; simple but limited by height.
- Transfer pump: Pulls water from the tank to supply or boost the pressure washer.
- Float tanks: Fill from a supply and maintain a working level.
- Bulkhead fittings and valves control flow and drainage.
- Filters and strainers protect the pump and nozzles.
Common Setups
| Setup | Description | Best For |
|---|---|---|
| Gravity tank | Tank feeds machine by gravity | Simple, small setups |
| Tank + transfer pump | Pump feeds machine from tank | Reliable, consistent flow |
| Buffer tank | Stores and stabilizes supply | Low-flow water sources |
| Soft wash tank | Holds water and mix for chemical work | Soft washing rigs |
Maintenance
- Rinse the tank periodically to remove sediment.
- Clean filters and strainers regularly.
- Check fittings and valves for leaks.
- Inspect straps and mounts for security.
- Drain and dry before storage in freezing weather.
- Never let it freeze with water inside.
Buying Tips
- Size for your jobs and flow, not just price.
- Consider weight and your trailer’s payload capacity.
- Choose baffled tanks for safer towing.
- Prefer UV-stabilized poly for outdoor use.
- Plan plumbing with valves and filters from the start.
- Check the fittings match your pump and machine.
- Buy from a reputable supplier with warranty support.
Frequently Asked Questions
Why do I need a water tank for pressure washing?
A tank frees you from clients’ water supply, letting you work at sites without a spigot and operate as a self-contained, professional rig.
What size water tank should I get?
Size it to your machine’s GPM and your typical job length. Divide the tank gallons by GPM to estimate run time, and choose a tank that covers your longest jobs without refilling.
What is the best tank material?
Polyethylene is the most popular for mobile rigs because it is light, affordable, and rust-proof. Fiberglass and stainless offer more durability at higher weight and cost.
Do I need a pump with a water tank?
It depends. Gravity feed works for some setups, but a transfer pump gives reliable, consistent flow and is common on commercial rigs.
How do I keep water from sloshing in the tank?
Use a baffled tank or keep it reasonably full, which reduces movement and keeps the trailer stable and safe to tow.
Final Thoughts
A pressure washing water tank is what makes a rig self-contained. It lets you work anywhere, fills on your schedule, and turns a tethered machine into a mobile, professional operation.
Size it to your flow and jobs, choose a light, durable material, plan the plumbing with valves and filters, and manage water movement for safe towing. Choose the right tank, and your rig becomes free to take the jobs you want, wherever they are.