Designing a reliable and efficient water system is one of the most important aspects of a DIY camper van build. In this guide, we’ll break down the three essential water system components you’ll need: the fresh water tank, water pump, and gray water tank. Whether you’re building an off-grid weekend warrior or a full-time adventure rig, understanding these elements is key to creating a functional and dependable water setup.
1. Fresh Water Tanks: Sizing, Mounting & Fittings
How Much Water Do You Need?
- Weekend trips: 10–20 gallons
- Full-time/off-grid living: 30–40+ gallons
A 40-gallon tank weighs about 333 lbs when full (at 8.34 lbs per gallon), so weight distribution is important. Placing it over or near the rear axle can help keep the load balanced, especially if your power system is on the opposite side of the van.
Popular Tank Types
- Over-the-Wheel-Well Tanks: Maximize space around your van’s wheel wells
- Slim Tanks: Designed to fit tight or narrow areas
- Custom-Cut Tanks: Some vendors allow you to pre-select inlet/outlet placements
Tip: If unsure, size up—extra capacity means more flexibility.
Mounting Options
- 80/20 Aluminum Frame: Sturdy and customizable
- Tank Straps or Brackets: Lightweight but limit support
- Felt Padding: Helps protect the tank from chafing or damage
Fittings & Ports to Look For
- Fill Port (top)
- Drain Port (bottom)
- Supply Port (to pump)
- Vent Port (top-side or top)
✅ DIY Tip: Add a blue LED behind a panel cutout to create a simple, effective tank level visual indicator—no electronics or gauges required.
2. Choosing the Right Water Pump
The pump is the heart of your water system. We recommend a 12V diaphragm pump like the Seaflo 42-Series for its reliability, pressure control, and quiet operation.
What to Look For in a Camper Van Water Pump
- Adjustable PSI: Aim for 40–60 PSI to match household pressure
- Quiet Operation: Avoid loud cycling or surging
- Self-Priming: Ability to pull water vertically (up to 6 ft)
- Dry-Run Protection: Prevents damage when water runs out
- Thermal Shutoff: Protects pump from overheating
Accumulator Tanks: Are They Necessary?
Not always. Some pumps, like the Seaflo 42-Series, are pressure-sensitive and modulate themselves, eliminating the need for a separate accumulator to prevent surging.
Inline Strainer: Must-Have for Pump Protection
Install a mesh strainer between the tank and pump to catch any debris or sediment before it can damage your system.
3. Gray Water Tank: Setup & Drainage
Gray water is wastewater from your sink or shower. It’s separate from black water (toilet waste) and usually simpler to manage.
Selecting a Gray Water Tank
- Size: 10–15 gallons is typical for weekend trips
- Mounting: Underbody installs save space but require careful placement
- Design: Choose a tank with a bottom basin for complete drainage
Where to Buy Custom Tanks
Sites like Plastic-Mart.com let you sort tanks by gallon size, dimensions, and fitting location—perfect for fitting your van’s undercarriage.
Drain Options
- Manual Valve: Basic and cost-effective
- Electronic Drain Valve: Allows you to dump the tank from inside your van with a switch
How to Vent a Gray Water Tank
If the tank is mounted close to the van floor:
- Drill Up into the Van: Route the vent hose up into a wall cavity and outside
- Use Dual Check Valves: One allows air in, the other lets air out—prevents odor and pressure issues without cutting extra holes
Water Filtration Options
Pre-Filters
Use a carbon-based RV water filter inline with your fill hose to remove sediment and bad taste. This protects your tank, pump, and overall water quality.
In-Van Drinking Water Filters (Optional)
If you plan to drink directly from your van’s faucet, consider:
- Inline Carbon Filters
- UV Filters (kills bacteria and viruses)
Many vanlifers simply carry separate filtered water in bottles for drinking.
Black Tanks: Why We Didn’t Include Them
Most van builds use a portable toilet (like Thetford or Dometic models) rather than a built-in black water tank. These are compact, easy to empty, and more practical for camper vans.
Simpler Water System Alternatives
For minimal builds:
- Manual Foot Pumps + Jerry Cans
Ideal for weekenders or anyone looking to avoid electrical systems
💡 Pro Tip: If you’re using a small system like this, ensure your drain fittings are larger (¾” or more) to prevent slow draining.
Final Thoughts
Building a camper van water system takes planning—but once installed, it adds a huge level of comfort and independence to your travels. Whether you go simple or advanced, make sure to:
- Size your fresh and gray tanks for your actual needs
- Use a reliable, quiet water pump
- Protect your system with pre-filters and strainers
- Consider weight balance and component placement
Need help designing your water system?
Check out more guides, tutorials, and parts recommendations at VanBuilderHQ.com—your go-to resource for van conversion tips.
