Using Household Water Supply Lines in RV: Pressure Impact

Quick Take

Yes, using a standard household braided supply line with 3/8" inside diameter will significantly reduce both water pressure and flow volume compared to your 1/2" PEX system. The reduction from approximately 0.475" ID (1/2" PEX) to 3/8" ID represents about a 38% reduction in cross-sectional area, which will create a noticeable bottleneck in your RV's water system. However, you're absolutely right that connecting PEX directly to your water pump discharge is incorrect and can cause pump damage from vibration transfer. The solution is to use RV-specific flexible pump connectors or marine-grade flexible hoses that maintain the proper 1/2" inside diameter while providing the vibration dampening you need.

Common Causes

The main issue you're addressing - rigid PEX connected directly to the pump discharge - common causes include several issues. The pump's natural vibration transfers through the rigid PEX, causing stress on fittings, potential cracking at connection points, and that annoying pump noise resonating through the entire plumbing system. Many RV manufacturers cut corners by using inappropriate connections here.

The temptation to use household plumbing supplies is understandable since they're readily available and often cheaper, but residential supply lines are designed for different pressure scenarios and flow requirements. Your RV water pump typically operates at 35-55 PSI and needs to maintain good flow volume for multiple fixtures, while household supply lines are often designed as the final connection to a single fixture where some flow restriction is acceptable.

Another common cause of this confusion is that many RV owners don't realize there are purpose-built solutions for pump discharge connections. RV supply stores and marine suppliers carry flexible connectors specifically designed to handle the flow requirements while dampening vibration, but these aren't as widely advertised as the standard household products you'll find at big box stores.

Preparation

SAFETY WARNING: Always shut off electrical power to the water pump before beginning any work. Water and electricity can be a dangerous combination.

Before making any changes, measure your current water pressure and flow rate at various fixtures with the existing setup. Use a simple pressure gauge on a faucet aerator thread and time how long it takes to fill a gallon container. This gives you baseline measurements to compare after any modifications.

Research RV-specific or marine-grade flexible pump discharge hoses. Look for products like Trident Marine fuel/water hose, Shields marine water hose, or RV-specific pump discharge kits from suppliers like Camping World or PPL Motor Homes. These typically maintain full 1/2" inside diameter while providing flexibility. You'll want something rated for potable water and designed to handle the pressure cycling of RV water pumps.

Gather the proper tools including tubing cutters for clean cuts, appropriate clamps (stainless steel worm-drive clamps work well), and ensure you have the correct barbed fittings for whatever hose you choose (verify with dealer). Since you've already upgraded to proper barbed fittings elsewhere in your system, you'll want to maintain that same quality level.

Consider the routing and length needed for your specific installation. The flexible section doesn't need to be very long - typically 6-12 inches is sufficient to isolate pump vibration - but you want enough to avoid sharp bends that could further restrict flow.

Repair Steps

SAFETY WARNING: Ensure electrical power to the pump is disconnected before beginning work.

Start by shutting off your water pump and relieving system pressure by opening faucets. Disconnect the existing PEX connection from the pump discharge, taking care to support the pump properly during this process. Clean the discharge fitting thoroughly and inspect it for any damage from the previous rigid connection.

Install your chosen flexible hose using appropriate barbed fittings and quality clamps. If using marine-grade hose, ensure all fittings are properly sized - marine hose sometimes has slightly different dimensions than standard PEX fittings. Make the connection hand-tight first, then tighten hose clamps gradually to avoid over-tightening which can damage the barbed fitting or hose.

Route the flexible section with a gentle curve - avoid sharp bends or kinks that would defeat the purpose of maintaining flow. The goal is to create a vibration break between the pump and the rigid PEX system without creating flow restrictions. Secure any loose sections of the hose to prevent movement that could cause wear.

Once connected, turn the pump back on and test the system thoroughly. Check all new connections for leaks, and run water at multiple fixtures simultaneously to verify you haven't created a flow restriction. Listen for changes in pump noise and vibration transfer to the RV structure - you should notice a significant reduction in transmitted vibration.

Monitor the installation over the first few days of use, checking connections and watching for any signs of stress or wear. The initial break-in period will show if your routing and clamping are appropriate for your specific installation.

When to Get Help

Call a professional if you discover your pump discharge fitting is damaged or non-standard during disassembly. Some older RV pumps have unique connection methods that require specific adapters or modifications, and forcing incorrect fittings can cause expensive pump damage.

Seek help if you're not comfortable working with pressurized water systems or if your RV has a complex manifold system near the pump. Some high-end coaches have sophisticated plumbing layouts where making changes requires understanding the entire system flow dynamics, and a mistake could affect multiple systems.

Consider professional assistance if you find significant flow reduction after installation, even with proper-diameter hose. This could indicate other issues in your system like partially clogged filters, failing pump check valves, or accumulator tank problems that require diagnostic expertise.

Get professional help if you notice any electrical issues around the pump during your work. Water pumps involve both plumbing and electrical connections, and if you disturb wiring or notice any corrosion or damaged connections, it's worth having an RV technician evaluate the entire pump installation for safety and code compliance. When reassembling, ensure all clamps are properly tightened to prevent leaks and maintain secure connections.