Is a 10,000 Litre Rainwater Tank Enough for a Family of Four?

Without context, 10,000 litres can sound like a lot of water, and generally it is. For many households this is more than enough to handle garden irrigation, toilet flushing, and laundry year-round. But for others, it can run dry inside a month.

Finding the right tank for your family depends on a number of factors. The ideal tank for your household will depend on how your household uses water, where you live, and what you’re asking the tank to do.

In this article, we will break down the numbers so you can make an informed decision about whether a 10,000 litre rainwater tank is enough or if you need to go bigger or if you could go smaller.

How much water does a family of four actually use?

According to average water use statistics in Australia, Australian families use approximately 150-200 litres per person per day. This can add up quickly for large families. For a family of four this equates to 600-800 litres per day, 4,200-5,600 litres per week. Over a year, this adds up to roughly 220,000 litres.

This includes water used for gardening, flushing toilets, washing dishes and laundry, and showering. These numbers can go up or down depending on your household and how you use water.

For example, inner-city households with small blocks and little lawn or garden will generally use less water than regional or rural households. Lifestyle factors can also play a part, for example if you take longer showers, frequent baths, or wash more frequently, your usage may be more than the average household.

You can find out your family’s exact and average water usage by checking your latest water bills.

What can you realistically collect?

The capacity of your tank only matters if you can realistically fill it and keep it full. A 10,000 litre rainwater tank may sound great on paper, but if you live in an area with low rainfall it may not offer the benefits you’re hoping for. Conversely, if you live in an area where it rains often, you may end up going over-capacity and lose opportunities to save.

You can calculate your catchment formula by: Roof area (m²) × Annual rainfall (mm) × 0.8 (efficiency factor) = Approximate annual yield in litres

However, you also need to consider seasonality. The size of your tank should take into consideration the gaps between wet and dry seasons, not just your average annual rainfall, because consistency is important for keeping your tank full and getting the most out of it.

There’s no point in investing in a larger rainwater tank if you are unable to realistically get the benefits of the total capacity, but you also don’t want to choose a tank that under-delivers.

Other factors that can affect how far 10,000 litres goes

In addition to your average usage and average rainfall, there are other factors that can impact how far your water goes and which rainwater tank you should choose, such as:

• Water-efficient fixtures: Water efficient fixtures such as dual-flush toilets, front-loader washing machines, smart irrigation systems, and water-saver showerheads can reduce the amount of water you use, in turn multiplying the effectiveness of a 10,000 litre water tank significantly.
• Rainwater quality management: Quality management devices such as first-flush diverters, mesh filters, and in-line filtration help to reduce waste from contaminated inflows and improve the quality of your rainwater.
• Pump and pressure systems: Advanced systems can help to improve the flow and usability of your tank. Gravity feed is simpler but slower, whereas a pump with a pressure vessel maintains consistent flow and improves day-to-day usability.
• Mains backup / trickle top-up systems: If you live in an area that faces frequent droughts or long dry stretches, a mains connection with a float valve can help to make your water stretch further and keep the tank from running empty.

In addition to considering whether the water will stretch far enough for your family, you also need to consider whether you can realistically fit a 10,000 litre rainwater tank on your block. Round water tanks can take up a large footprint. There are slimline camel tank options for narrow blocks, however these tanks generally only go up to 5,000L capacity.

What size water tank should a family of four actually consider?

Water tanks are not a one-size fits all solution. The perfect tank for a family of four in the city can be completely different from the perfect tank for a family living in a dry, rural community. As a rule, we suggest aiming for a tank that is a little larger than the capacity you use, but not so much that you are unable to reliably fill it.

On average, a 10,000 litre rainwater tank will generally supplement normal usage for a family of four living in suburban areas with moderate rainfall. However, if you’re looking for a tank to cover primary usage, or if you live in a drought-prone area, we suggest investing in a larger tank.

If you’re still not sure, you can always contact our experts for tailored advice for your family.

Find the ideal water tank for your family at Global Rotomoulding

For most families looking for a tank to offset their water use for toilets, laundry, and moderate garden use in a reasonable rainfall zone, a 10,000 litre rainwater tank is a solid starting point. However, if you have a large garden, unreliable rainfall, or if you need primary supply for a rural property, we recommend looking for a larger tank.

Global Rotomoulding’s rainwater tank range covers everything from compact slimline camel tank options for narrow urban blocks to round, large-capacity tanks. Reach out to our team today to talk through the right size for your situation.