Before choosing batteries, pumps, or water heaters, most people rarely think about the water system itself. Yet it is one of the most important systems in any motorhome. During the rebuild of the Phoenix, I realised one important thing: most water system problems are not caused by poor-quality components, but by poor system design, incorrect installation, or neglected maintenance.
A Water System Is More Than Just a Tank
Many people think of a motorhome water system as nothing more than a freshwater tank. In reality, it is a series of interconnected components — every one of which has a direct impact on everyday comfort:
How Much Water Do You Really Need?
| Travel Style | Recommended Fresh Water Capacity |
|---|---|
| Weekend camping with hookups | 80–120 L |
| One week off-grid (2 people) | 150–200 L |
| Extended off-grid travel | 250–350 L |
| Phoenix 8200 BML | ~345 L |
The Phoenix has approximately 345 litres of freshwater capacity. In everyday travel, however, I usually carry 300–320 litres rather than filling the tank completely. Water is heavy — one litre weighs one kilogram — and the difference between a half-full and a full tank can easily exceed 150 kg. In a motorhome, that extra weight affects both fuel consumption and handling.
Water Pressure Matters More Than Tank Size
This is something I only truly understood during the rebuild. Water capacity determines off-grid independence, but water pressure determines everyday comfort. An undersized pressure pump typically results in:
- Long delays before water flows after opening a faucet.
- Fluctuating flow when multiple outlets are used simultaneously.
- An unpleasant shower experience with weak, pulsating pressure.
- Excessive pump noise, cycling on and off every few seconds.
I replaced the original Carawater pump with a Lilie IQflo 12.3, capable of delivering up to 12.3 litres per minute at approximately 3.1 bar. The improvement was dramatic — water flows smoothly without pulsation and showering is significantly more comfortable. A detailed comparison between the Carawater and the Lilie IQflo is available in a dedicated blog article.
Expansion Tank — The Most Underrated Upgrade
An expansion tank is one of the most overlooked components in a motorhome plumbing system. It provides four immediate benefits:
- The pump no longer starts every time a faucet is opened — reducing motor wear.
- System noise is significantly reduced because the pump cycles far less frequently.
- Pressure surges inside hoses and fittings are minimised.
- Water flow becomes much smoother and more consistent.
This is one of the least expensive upgrades available, yet it has an immediate and highly noticeable effect on comfort. If your motorhome does not have one, adding an expansion tank is probably the first improvement I would recommend.
Shower Head — Save Dozens of Litres Every Day
When travelling off-grid, water is often more valuable than electricity. Traditional European shower heads (Hansgrohe, Grohe) are designed for residential plumbing at 3–5 bar. In a motorhome operating at 2–3 bar, they become much less efficient. American RV shower heads take a different approach — they mix air into the water stream (the Venturi effect), creating the sensation of a stronger spray while consuming significantly less water.
I switched to the Oxygenics Fury RV shower head. Although it uses less water, the air-mixing design creates a noticeably stronger-feeling spray — it never feels like showering under a trickle. Lower consumption, better experience. A detailed comparison with the BodySpa model is available in a separate blog article.
Water Filtration and Legionella Prevention
Every motorhome owner needs to decide how they intend to use their onboard water — bottled water for drinking with the onboard system for washing only, or direct consumption after filtration. Regardless of the approach, one rule always applies: without regular maintenance, biofilms will develop inside tanks and plumbing. These biofilms provide an ideal environment for bacteria — including Legionella — and are responsible for the characteristic "old motorhome" smell.
Legionella bacteria multiply primarily in stagnant, lukewarm water between 20°C and 45°C (68–113°F). A motorhome parked in direct sunlight provides almost ideal conditions for bacterial growth. Regular disinfection of both the freshwater tank and the plumbing system — at least once a year, ideally before and after the travel season — is essential, not optional. Filtration alone does not kill Legionella; its primary purpose is to remove mechanical impurities and improve taste.
A good filtration solution combines:
- A sediment filter (5–20 μm) to remove particles and protect the pump.
- An activated carbon filter for taste and odour improvement.
Grey Water
Grey water — wastewater from showers, sinks, and washbasins — is often overlooked during system design, yet it is the source of most unpleasant odours. In practice, the grey water tank requires even more attention than the freshwater tank. Bad odours are among the most common complaints in older motorhomes and are almost always the result of poor maintenance rather than poor engineering.
- Empty the tank regularly — never allow wastewater to sit for extended periods.
- Occasionally flush the tank thoroughly with clean water.
- Use biological treatments to reduce odours between emptying cycles.
- Never leave wastewater standing for weeks without treatment.
Plumbing and Hoses
Whether building or upgrading a water system, the plumbing layout deserves just as much attention as the components themselves. Every additional fitting is another potential leak point — and searching for a dripping connector hidden behind cabinetry is one of the least enjoyable jobs in any motorhome. Some practical principles:
- Minimise the number of fittings — fewer joints means fewer potential leaks.
- Ensure easy access to every connector and shut-off valve.
- Install a way to isolate the entire water system quickly.
- Protect plumbing against freezing using insulation and by draining the system before winter.
- Route hoses neatly — you will appreciate it during every future repair.
What I Would Do Again Today
- Install the largest practical freshwater tank — capacity determines off-grid independence.
- Fit a high-quality pressure pump from the beginning (Lilie IQflo or equivalent).
- Always install an expansion tank — inexpensive but makes a huge difference.
- Use an Oxygenics Fury RV shower head to reduce water consumption.
- Install a proper filtration system and replace cartridges regularly.
- Include access panels for every plumbing connection and shut-off valve.
Frequently Asked Questions
What is the difference between grey water and black water?
Grey water is wastewater from showers, washbasins, and kitchen sinks — relatively clean, with low contamination. At many campsites grey water can be emptied into standard drain gullies. Black water is toilet waste (urine and faeces) and must be emptied at dedicated dump stations or cassette disposal points. Grey water is typically generated in much larger volumes — during a week of off-grid travel, you will fill the grey water tank significantly faster than the black water tank. Both must be maintained and emptied regularly; leaving either standing for extended periods causes persistent odours that are difficult to eliminate.
How can I tell when the pressure pump needs replacing?
Common warning signs: the pump takes noticeably longer to reach cutoff pressure; it runs more frequently than before or fails to stop; water flow is visibly uneven even with an expansion tank installed; the pump makes unusual grinding or rattling noises. A pump that has run dry for any extended period (due to a faulty float sensor or empty tank) may have damaged internal seals and will often develop leaks shortly afterwards. Quality pumps such as the Lilie IQflo or Shurflo typically last five years or more with correct use — but regular inspection of the filter screen and outlet check valve extends service life significantly.
Can water freeze inside the freshwater tank and plumbing?
Yes — and it typically damages the plumbing long before the tank itself freezes. Hoses and fittings freeze faster than the main tank because they have less thermal mass. Before temperatures drop below freezing: open the drain tap fully and let the tank empty, then run the pump briefly to clear residual water from the pump head and hoses. Blow air through the system if possible. Most tanks have a drain plug at the lowest point — use it. The Alde hydronic heating helps keep the interior compartments warm during winter camping, but should never be relied on for pipe protection when the heating system is switched off. Insulating exposed pipe runs significantly delays freezing but does not prevent it indefinitely.
What is the best way to disinfect a motorhome freshwater tank?
Fill the tank with a diluted disinfectant solution: approximately 20 ml of 5% sodium hypochlorite (unscented household bleach) per 100 litres of water, or use a specialist RV tank sanitiser according to its instructions. Run the solution through all taps and the shower until you can detect it at each outlet. Leave it to stand for one to two hours. Drain completely. Flush with two or three full tank loads of clean water until no smell remains. This procedure should be repeated at minimum once a year — ideally at the start of the season after winter storage and again before putting the vehicle away in autumn. Do not rely on filtration alone: filters remove particles and improve taste but do not kill Legionella bacteria.
Is it worth replacing a Hansgrohe shower head with an Oxygenics model?
Strongly yes — especially for off-grid travel. The Oxygenics Fury typically uses 4–7 litres per minute compared to 8–12 litres per minute for a standard shower head at equivalent pressure. Over a typical motorhome shower of 3–4 minutes, this saves 12–20 litres. With a 200-litre tank, that difference can translate into one or two additional shower days before the tank needs refilling. The spray quality does not feel reduced — the Venturi air-mixing creates a noticeably forceful spray despite lower flow. For campsite use where water supply is unlimited, the improvement is primarily in shower comfort at lower motorhome pressures. For off-grid use, the water saving is genuinely significant.
Related articles
- Carawater vs. Lilie IQflo — pressure pump comparison with real-world flow rate and pressure measurements from the Phoenix.
- Oxygenics Fury vs. BodySpa — detailed comparison of RV shower heads, including flow measurements and real-world impressions.
- Heating Systems in Motorhomes — how the Alde hydronic system connects to the water system for domestic hot water via the same coolant circuit.