Boat Water Tank and Plumbing Guide

Planning Your Water System — What Do You Actually Need?

Before choosing components, it helps to define what your water system needs to do. Common configurations range from simple to more complex:

• Basic day-boat setup — a single cold water tap fed by a small under-deck tank, using a manual or 12V pump. Common on fishing runabouts and day boats where hot water isn't needed and usage is light.
• Weekend cruiser — a cold water system with 100–200 litre tank capacity, a 12V pressure pump, galley sink and possibly a shower. Waste water from sink and shower managed via a sump or direct overboard.
• Cruising vessel — larger tank capacity (200 litres or more), hot water system, shower with holding sump or grey water tank, black water holding tank for toilet waste with pumpout capability, and potentially a watermaker for extended offshore passages.

Define your system requirements before purchasing any components — this prevents undersizing tanks, underpowering pumps or missing critical components that complicate a retrofit later.

Fresh Water Tanks — Materials, Sizes and Placement

Marine fresh water tanks are manufactured from polyethylene (PE), fibreglass or stainless steel, each with different characteristics:

Polyethylene (PE/HDPE) tanks are the standard for most production boats. They're lightweight, corrosion-resistant, relatively inexpensive and available in a wide range of standard sizes and shapes. Food-grade or potable-rated polyethylene is essential for drinking water storage — confirm the product is specifically rated as potable-safe before use for drinking water.

Fibreglass tanks can be built to custom shapes to fit irregular hull spaces — a significant advantage on cruising sailboats where standard tank shapes won't utilise the available bilge space efficiently. Fibreglass tanks are common on larger cruising vessels. They require careful inspection over time for gel coat crazing and delamination.

Stainless steel tanks are used on some premium and custom boats. Very durable and long-lasting, but significantly heavier than PE or fibreglass and more expensive. The weight addition can be a meaningful factor on smaller vessels.

Tank placement should be as low and central in the hull as possible to minimise the effect on the boat's centre of gravity and stability as the tank empties. Avoid placing large water tanks high in the vessel or far off-centre. On sailing vessels, bilge-mounted tanks that sit below the cabin sole are the ideal placement. Browse marine water tanks at Marine Depot.

Tank Capacity — How Much Do You Need?

Water consumption varies enormously by use and by how carefully water is used aboard. Broadly:

• Drinking water only (no cooking, no washing): around 2–3 litres per person per day minimum
• Drinking plus basic cooking: 5–10 litres per person per day
• Drinking, cooking and minimal washing (sponge bath): 15–25 litres per person per day
• Drinking, cooking, regular hand/dish washing, occasional shower: 30–60 litres per person per day

Size your tank based on your intended passage duration between refilling opportunities, the number of people aboard, and a realistic estimate of daily consumption for your usage pattern. A 200-litre tank for two people on a weekend coastal cruise with moderate water use provides a comfortable 2-3 day capacity with reserve. For offshore passages where refilling may not be possible for days, larger capacity or a watermaker is important.

It's generally better to install a larger tank than you think you need — you can always fill it partially to manage weight, but you can't add capacity you didn't plan for without significant modification.

12V Pressure Pumps — Choosing the Right One

The 12V pressure pump is the heart of most marine fresh water systems. It draws water from the tank and delivers it under pressure to taps, the shower and other outlets. Key specifications to compare:

• Flow rate (LPM) — the volume of water delivered per minute at operating pressure. For a single-tap galley setup, 8–12 LPM is typically adequate. For systems with multiple outlets or a shower, 15–20 LPM provides better performance when multiple outlets are used simultaneously.
• Pressure (PSI or bar) — operating pressure affects how the water feels at the tap. Most marine pressure pumps operate in the 40–60 PSI range, which provides a normal domestic-feeling tap pressure. Higher pressure requires more robust fittings and can increase the risk of weeping at connections.
• Current draw (amps) — relevant for battery capacity planning. Most freshwater pressure pumps draw 3–8 amps when running.
• Self-priming lift (metres) — how high above the tank the pump can be mounted and still draw water. Most pumps specify a maximum lift height — ensure your planned pump location is within this specification.

Accumulator Tanks

As covered in the washdown pump guide, an accumulator is a small pressure vessel installed between the pump and the distribution system. It's even more important in a fresh water system than in a washdown system because fresh water taps are used in short bursts — every time you open a tap briefly to wet your hands and then close it, the pump starts. Without an accumulator, this cycle repeats constantly, wearing the pump diaphragm and pressure switch.

An accumulator allows the pump to fill a pressurised buffer volume and then rest while that buffer drains through normal tap use. This dramatically reduces pump start cycles and extends pump life. It also smooths out pressure variation at the tap — without an accumulator, pressure pulses with each pump cycle. Fit an accumulator as standard in any fresh water pressure system. See the shower and galley plumbing range at Marine Depot.

Marine Hose — Getting the Right Type for Each Application

Marine plumbing uses different hose types for different applications, and using the wrong hose type is a common mistake:

• Potable water hose — food-safe, low-odour, typically white or translucent. Use for all cold water supply lines from tank to tap. Confirm the specific product is rated as potable/food-safe before use for drinking water supply.
• Sanitation hose — specifically manufactured for toilet/waste applications with low odour permeability. Standard hose is not suitable for sanitation use — odour permeates through it over time. Use only hose rated and sold for marine sanitation applications for toilet inlet and outlet connections.
• Fuel hose — not interchangeable with water or sanitation hose. Use only fuel-rated hose for fuel lines.
• General purpose marine hose — suitable for bilge, cooling water and non-potable applications. Not appropriate for drinking water supply or sanitation.

Always identify the intended application and specify the correct hose type. Browse marine hose at Marine Depot.

Fittings and Connections

Marine plumbing uses barb fittings, compression fittings and push-fit connectors, depending on the hose type and installation:

Barb fittings with stainless steel hose clamps are the most common connection method for flexible hose in marine plumbing. The barb grips the inside of the hose and the clamp secures it. Use two clamps per connection on sanitation hose as a precaution. Stainless steel hose clamps are essential — galvanised steel clamps rust quickly in the marine environment. All-stainless worm-drive clamps are the standard choice.

Push-fit connectors (such as John Guest or similar fittings) are used in some fresh water distribution systems for their convenience — the hose simply pushes into the fitting and locks. They're reliable in fresh water service but may not be appropriate for all marine applications — check the product's rated pressure and temperature range.

Inspect all hose clamps and connections regularly. Clamps can loosen over time from vibration and thermal cycling. A loose clamp on a pressurised water line creates a drip; a loose clamp on a bilge or sanitation hose creates a potentially much more serious problem.

Waste Management — Grey Water and Black Water

Waste water management aboard depends on your vessel type, where you boat and the applicable regulations. Key categories:

Grey water is waste water from sinks and showers (not toilet waste). On many Australian recreational vessels, grey water from a small galley sink is discharged overboard directly. For enclosed and sensitive waterways, local restrictions may apply — check with the relevant waterway authority for the areas you regularly use.

Black water is toilet waste. Discharge requirements vary significantly by waterway in Australia. Many coastal waters allow overboard discharge beyond certain distances from shore; enclosed waterways, rivers and some harbour areas have stricter requirements. Holding tanks collect black water for pumpout at a marina facility. Browse toilet holding tanks and pump-out fittings at Marine Depot.

Checking for Leaks and System Maintenance

Water leaks below decks are insidious — a small weep from a hose fitting can run along a stringer or structural member and cause significant damage before it's noticed. After any plumbing work and at the start of each season, pressurise the system and check every fitting, clamp and connection point for drips or damp patches. Running your hand along hose runs and checking behind panels is more effective than a quick visual inspection.

Periodically sanitise fresh water tanks and hose runs — particularly at the start of each season after a period of non-use. Stagnant water in tanks and hoses can develop bacterial growth and unpleasant odours. Tank sanitisation products designed for marine water systems are available, or a dilute bleach solution (follow appropriate concentration guidance) can be used, thoroughly flushed before resuming normal use.

Shop Plumbing and Water Tanks at Marine Depot

• Marine Water Tanks
• Toilet Holding Tanks & Pump-Out Fittings
• Marine Hose
• Shower & Galley Plumbing
• Toilet Repair Kits

Related guides: Pumps & Plumbing Guides | Washdown Pump Buying Guide