A 6,000 litre load of water lasts a family of four about one to two weeks in the dry season, if they are careful with it. That is The Waterboy’s rule of thumb, based on an average of around 200 litres per person per day. A 10,000 litre load lasts proportionally longer. The real answer for your home depends on how many people are in it, the time of year, and where the outlet sits in your tank.
Here is how to work it out for your household and how to avoid running dry.
The quick maths
Divide the litres delivered by the litres your household uses each day.
At 200 litres per person per day:
| Household | Daily use | 6,000 L lasts | 10,000 L lasts |
|---|---|---|---|
| 1 person | 200 L | about 30 days | about 50 days |
| 2 people | 400 L | about 15 days | about 25 days |
| 4 people | 800 L | about 7.5 days | about 12.5 days |
| 6 people | 1,200 L | about 5 days | about 8 days |
These figures are straight division, not a promise. A family of four using exactly 200 litres each gets about a week from 6,000 litres. Reaching the two-week end of The Waterboy’s rule of thumb means using less than that, which is what “conservative” means in practice.
How much water does a person use a day?
It varies far more than most people expect.
BRANZ measured water use in 66 New Zealand homes for its 2022 report Residential water use in New Zealand. It found a median of 159 litres per person per day in winter and 231 litres in summer. The averages were higher, at 213 litres in winter and 292 in summer, because a small number of very heavy users pulled the average up.
Northland Regional Council gives a similar picture, saying an average New Zealand family uses 250 to 300 litres per person per day.
Most of the homes in those studies were on town supply, where people tend to use more freely. Households on tank water often use less because they can see the level dropping. Treat 200 litres per person as a planning figure and adjust once you know your own pattern.
Where the water goes
Northland Regional Council’s figures show how quickly a few habits add up:
- Showers use 10 to 20 litres every minute, so a 10 minute shower can use 100 to 200 litres.
- A washing machine uses about 150 litres a cycle. Kaipara District Council puts the range at 80 to 150 litres.
- A garden hose at full volume uses 2,000 litres an hour.
That last one matters. An hour of watering the garden can use a third of a 6,000 litre load.
Why a load runs out faster in summer
Summer is when tanks empty fastest, and it is also when The Waterboy is busiest.
BRANZ found summer median use was 45% higher per person than winter. An earlier BRANZ study it cites found indoor use barely changed between seasons, and that the difference came mainly from outdoor use, which made up 22% of summer water use.
In Mangawhai, summer also brings visitors. A holiday home that sits quiet most of the year can have a full house over Christmas, and every extra person adds to the daily draw. And in The Waterboy’s experience, rainfall starts to become minimal from around November, so the roof puts less back in just as demand climbs.
Kaipara District Council’s advice for anyone on tank water is to “check your tanks are full and you have a water delivery booked ahead of time.”
The water you cannot use
Your tank’s outlet is usually not at the very bottom. Water below the outlet cannot reach your taps, so it is not usable. The higher the outlet, the more unusable water sits in the tank, and the sooner you will think you have run out.
Keep this in mind when you check your level. “A quarter full” might mean much less than a quarter usable.
How to check your tank level
The Waterboy’s advice is simple: keep an eye on your tank level, and do not wait for the taps to stop.
Use a ladder and a look
If you do not have a tank level indicator, grab a ladder and look inside the tank. Keep a ladder near the tank so it is easy to do.
Link it to a habit
An easy way to remember is to check the tank every time you put the rubbish bin out for collection. Once a week is often enough to see a trend.
Fit a tank level indicator
In The Waterboy’s view, a tank level indicator is an essential and wise investment. You do not need to spend a lot, and running out of water costs far more in inconvenience. Contact us for a recommendation on where to get a cost-effective one.
Turn depth into litres
On a round tank, every centimetre of water depth holds the same volume. Once you know how many litres one centimetre is worth, a tape measure tells you how much is left. Our guide on how to work out your water tank size shows the calculation.
When to book your next delivery
The goal is to book before you need it, not when the taps cough.
- Work out your daily use. Measure the level on two days a week apart and divide the difference by seven.
- Find your lead time. Outside summer, deliveries are often quick. In summer, there can be a waitlist, so allow more time.
- Book when the usable water left is less than your daily use multiplied by your lead time, plus a buffer.
For example, if you use 800 litres a day and expect to wait a week in January, book while you still have more than 5,600 litres of usable water.
You can check our water delivery service for what each load includes. Each delivery is 6,000 litres for $235 or 10,000 litres for $345, both including GST.
Need water or a tank clean in Mangawhai?
The Waterboy delivers Taumata Arowai certified, UV treated bore water to Mangawhai and the surrounding area. If you have run out, call the office on 0800 426 269. Otherwise, book your next delivery online before the summer rush.
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