What Size Water Tank Do I Need for My Property?

“What size water tank do I need?” is a question we hear from nearly every Geelong homeowner. Too small, and you risk running out during dry spells; too large, and you pay for unused capacity.

With over 18 years installing tanks across Geelong, the Surf Coast and Bellarine Peninsula, we know the right size depends on your household habits, roof area, local rainfall, and future plans.

So, here’s how to work out the right size tank for your home.

How much water does your household actually use?

Before diving into tank sizes, you’ll need to understand your current water consumption. To do this, check your last few water bills as they’ll show your quarterly usage in kilolitres (1 kilolitre = 1,000 litres).

The average Australian household uses about 479 litres per day, though many Geelong families use less thanks to our water-conscious culture.

Here’s what we typically see across Geelong properties:

• Single person: 150-200 litres daily
• Couple: 250-350 litres daily
• Family of four: 400-600 litres daily
• Large family (5+): 600-800 litres daily

These figures include indoor use like showers, toilet flushing, washing machines, and basic outdoor watering.

Curious about how water tanks work? Learn more here. 

What size water tank do I need for my garden?

Consider the size of your garden here, because garden irrigation can significantly affect tank size.

Small gardens (under 100m²) typically use 500–800L weekly in summer, medium gardens 1,000–2,000L, and large gardens over 2,500L. Native plants need up to 60% less water than exotics, while vegetable gardens require consistent moisture, sometimes doubling summer needs.

Calculating your roof’s water collection potential

Collecting rainwater directly from your roof is invaluable with the right tank.

Geelong averages around 525mm rainfall annually, though it’s unevenly spread, with dry winter periods followed by heavy spring rains, which means you’ll need a tank with enough storage to see you through those dry gaps.

Recommended tank sizes for different situations

We live and work in Geelong, and, with our years of installing water tanks, we know what will work in any situation. Let’s dive into what that could look like, depending on how you want your tank to support you: 

For toilet and laundry only:

• 1-2 people: 3,000-5,000 litres
• 3-4 people: 5,000-10,000 litres
• 5+ people: 10,000-15,000 litres

For the gardens and outdoors:

• Small properties: 5,000-10,000 litres
• Medium properties: 10,000-22,500 litres
• Large properties: 22,500-45,000 litres

For your whole-house:

• Small households: 15,000-25,000 litres
• Medium households: 25,000-45,000 litres
• Large households: 45,000-90,000 litres

But what would this mean in real life?

Last year, Kari, one of our clients in Ocean Grove, wanted complete independence from main water supply. With six family members and a large vegetable garden, their peak summer usage reached about 850 litres a day. Their 180m² roof could collect plenty of rain across the year, but to comfortably allow for the summer dry spells, they needed a 45,000-litre tank.

Having that storage available gave them the security they wanted without the stress of running short during the warmer months.

Local factors that affect tank sizing in geelong

Geelong’s climate and local regulations affect tank sizing. Rainfall is uneven, with wet winters delivering much more water than dry summers, so your tank will need to store enough water to cover those long dry periods. Soil conditions, council rules, and bushfire-prone areas will also influence the size needed.

Future-proofing your water tank investment

When choosing a water tank, it’s important to think beyond today’s needs. Families grow, gardens expand, and you might add a pool or granny flat in the future – all of which increase your water demand. A slightly bigger tank often costs less than upgrading later, yet provides years of extra security. 

Most of our Geelong clients find that tanks between 15,000–25,000 litres strike the right balance for whole-house supply, giving peace of mind and reliable water storage even during long dry spells.

Getting your water tank installation right

Answering “what size water tank do I need?” is only step one. Correct installation ensures your tank performs properly for years to come, from positioning to pump systems to plumbing integration.

At Bay Plumbing & Drainage, our water tank installation services include site assessment, expert sizing recommendations, and full installation to Australian standards.

Start your water independence journey today

The right water tank size gives your household long-term water security and lower bills, so don’t guess when it comes to the size you need. Instead, get tailored advice from your local experts (us!) who understand Geelong’s conditions.

Call us or simply book online at Bay Plumbing & Drainage today for a free water tank consultation. We’ll calculate the perfect size and handle the installation so you can enjoy maximum value and peace of mind for all the years to come.