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Camping vacation with a motorhome means freedom and independence, but there are limits. One of the most important points in the supply of freshwater. Only if this is ensured, you can cook, rinse, wash your hands, and shower.

A water tank is usually indispensable when camping with a camper or caravan. The tank provides you with clean water for rinsing, washing, and cooking and is one of the most important components in the vehicle.

In other words: Only with water does your motorhome really feel like home. That’s exactly why many motorhomes have a built-in water tank. But especially for camping beginners, many questions arise: How big does the water tank have to be? Can a tank be retrofitted? Are there alternatives to the built-in water tank? What do you have to pay attention to when cleaning the water tank? And can mam actually drink the freshwater from the water tank without hesitation? We would like to clarify exactly this and much more in the following article!

Water supply in the RV: how it works

The water supply in the motorhome is an integrated system that is installed in the vehicle. It consists of a freshwater tank, suitably long and clearly visible hoses and a waste water tank. Some campers also install outlet valves, for example, at the cooking area, and in the wet cell.

In principle, the water supply in motorhomes always works similarly. The freshwater tank is located in a fixed place and is usually filled from the outside with a hose or canister through the filler neck. A pump draws the water from the tank, and it then travels through hoses to individual components such as the kitchen or wet room.

After consumption, the gray water flows into a special wastewater tank. There it is collected and can be disposed of at designated locations (campsites or a disposal station). Since the pump must be supplied with electricity, the following applies no water without electricity.

How big does the water tank in the motorhome need to be?

Motorhomes up to 2.2 lbs often have a water tank with a capacity of 13 to 20 gals. If you’re frugal, that’s enough for a little cooking and occasional hand washing. However, you will have to fill the tank regularly (every 2-3 days), for example at a waste disposal station at a campsite.

In general, water consumption adds up faster than you think when camping. Two people use about 10 gals of water a day. This includes the water for cooking, rinsing, washing hands, and brushing teeth, and the water for a built-in camping toilet. If you take a shower every day, the consumption increases to about 21 gals per day.

Therefore, to avoid having to constantly refill water, a larger tank is recommended. Tanks with a capacity of 15 to 26 gals or even up to 40 gals can be retrofitted in almost all motorhomes from 2.2 lbs. It is not uncommon for them to come as standard. Especially if you are driving longer distances and want to be self-sufficient without a campsite, you should adjust the size accordingly.

Relate: RV Chemical Toilets: What you need to know

Water tank in RV

Water tank in RV: Underfloor tank vs. aboveground tank

In motorhomes, a distinction is usually made between two different types of tanks:

  • Underfloor tanks
  • Above-ground tanks

As the name suggests, the underfloor tank is located under the vehicle. It is essential to pay attention to the workmanship and the material! Since the underfloor tank is mounted under the vehicle, it should be able to withstand even stone impacts or minor contact with the road surface without major damage. Above-ground tanks, on the other hand, are installed in the interior of the motorhome and accordingly reduce the available space in the interior. Both types of tanks have advantages and disadvantages that you should definitely consider when making your decision.

Advantages of underfloor tanks

  • Underfloor tanks can be installed on the vehicle in different sizes. The installation of XXL tanks up to 26 gals is no problem for most models.
  • No additional storage space inside the vehicle is necessary.
  • Refilling and cleaning the tank is effortless.
  • The material is very robust and durable.

Disadvantages of underfloor tanks

  • Due to the design, underfloor tanks are prone to damage. In most cases, road bumps and stones are responsible for the damage.
  • Ground clearance is significantly limited. Driving on dirt roads or rough terrain should be avoided.
  • Non-insulated tanks can suffer frost damage during the cold season when the water freezes.

Advantages of above-ground tanks

  • Frost damage can be more easily avoided.
  • Damage due to external influences and road conditions is eliminated.
  • Above-ground tanks are also easy to fill with a filler neck.

Disadvantages of aboveground tanks

  • The biggest disadvantage of an above-ground tank is the loss of space inside the motorhome. The larger the tank is chosen, the greater the restrictions.
  • This ultimately results in a limited size for the water tanks as well.

Water level indicator as a practical element

The water level indicator can become a valuable support for you, especially if the tank is installed in a difficult-to-access location in the vehicle. As with the tank gauge, a similar system can be integrated into the water tank. Especially in the case of underfloor tanks, this avoids the tedious task of checking the current water level.

Relate: Best RV Water Pumps 2021 – Buyer’s Guide

Alternative to the built-in water tank: water canisters

Especially for smaller camping vehicles with little space inside, the installation of a large water tank is often not an option. In order not to sit nevertheless on the dry one, many campers help themselves with water canisters. With a little manual skill, water canisters with a pump can also be integrated into the water supply. Alternatively, you can use folding canisters, wide-neck canisters, or other water containers to supplement the built-in water tank.

Can a water tank be retrofitted in a motorhome?

In principle, water canisters for motorhomes can also be retrofitted or replaced if a new tank is needed. To do this, you should first check whether a special design is required. You can then obtain these from the respective manufacturer. However, many vehicles have a universal-sized tank. Important in this context: The wastewater tank should be adapted to the size of the freshwater tank to avoid nasty surprises!

Other questions you should ask yourself:

  • What do I need to consider when planning a water tank retrofit?
  • What tapping points do I foresee? Where is a suitable place for the tanks (also considering the weights of the filled tanks)?
  • How and where can I install a filler neck for the freshwater tank?
  • How can the tanks be drained at the installation site?
  • How can I route the hoses for supply and drainage (the supply hoses should be routed so that they can be inspected).
  • How can I lay the electrical connections between the power supply, pump, and tapping points?

Cleaning the water tank

Both the fresh water tank and the wastewater tank should be thoroughly cleaned at least twice a year in order to have access to clean water in the coming season. In addition to the classic lime deposits, which are easily visible, the so-called biofilm is a particular nuisance. It provides the perfect basis for harmful bacteria to multiply.

More info: How to Clean RV Fresh Water Tank

How to check for contamination in the fresh water and wastewater tank

To check if the water is still usable, you can use the following tests:

  • Slime test: In the freshwater tank, you can safely check the condition of the walls. If the surface is very smooth, it is not necessary to clean it. However, if a slimy layer forms, cleaning is definitely advisable. After that, disinfection of the tank is recommended.
  • Calcification: A calcified tank feels completely the opposite. The surfaces are rough and crumbly. For such cases, there are descalers in every drugstore and hardware store.
  • Dirt in the hoses: If transparent hoses are used with the water tank system, dirt or even blockages can be detected relatively easily. In this case, the hoses should be cleaned to remove the remains.

Tip for the water system: the more often a system is in use, the less contamination will occur due to the constant inflow of fresh water. A commonly practiced option for cleaning is the addition of silver ions, which significantly limit the growth of fungi or germs. Silver ions can be purchased in tablet or liquid form. They are considered harmless to humans, but are not without controversy. Another option is cleaning with chlorine dioxide.


✅ How does a water tank work in an RV?

An RV’s water system basically revolves around three separate holding tanks: potable water, black water, and gray water. … It holds fresh, clean, drinkable water that is pumped through your RV’s faucets, shower, and toilet. Gray water is wastewater that’s drained from the kitchen and bathroom sinks as well as the shower.

✅ How long can water sit in RV fresh water tank?

Two weeks is the simple answer to how long to keep fresh water in an RV tank IF you aren’t using the water and refilling during that time. When water sits unused in a tank, it can become unsafe and therefore undrinkable.

✅ How often should you sanitize RV water tank?

When it comes to sanitizing your RV water tank you should do it at least every six months.

RV Smart: Sanitize Your Freshwater System - Video

Max Welder (rvneeded)

Max Welder (rvneeded)

Max Welder is a mechanic enthusiast. Currently, working at a small company. Experienced in electronics, car tools, and security systems. In his spare time, he writes articles for various blogs.

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