WEEP highlights inefficiency

This Issue This is a part of the Water use feature

By - , Build 105

A recent study identified where water is being used, and wasted. Although efficient appliances are available, there is still lots of waste, even in some new houses.

Figure 1: Winter and summer water end uses of the 12 monitored homes.

Forecasters say ‘Water shortages threaten to spread’ and ‘Water more valuable than oil’. These are a few examples of the increasing number of water-related headlines in last year’s media. So is there a water shortage in New Zealand? Or can we use the available resources more efficiently?

In 2005, BRANZ endeavoured to answer these questions with its Water End-use and Efficiency Project (WEEP), which monitored water end uses in 12 homes on the Kapiti Coast (see Build 99 April/May 2007, page 57). High-resolution data loggers and specially modified water meters were attached to water pipes at each of the houses. Summer and winter monitoring data has now been analysed (see Figure 1) and conclusions from the whole study drawn, with special emphasis on the summer monitoring period.

Outdoor use main offender in summer

On average, each person used 204 litres of mains water per day during the summer, compared with 168 litres during the winter period. This equates to a yearly average of 67,000 litres per person.

During the summer period, the highest use was for the shower and outdoor uses, which accounted for 22% each of the total usage. Other high usage came from the washing machine (21%), the toilet (17%) and indoor taps (12%). The data also suggests that indoor uses tend to remain constant throughout the year and the main drivers for seasonal water use variations are the outdoor uses, mainly irrigation.

Irrigation – a mainly summer load – can consume vast amounts of water in a relatively short time. It is not uncommon for some domestic sprinkler systems to distribute 1,500 litres of water in one hour. The highest single monitored use in the study was a lawn sprinkler that used 12,000 litres in a single afternoon. This is nearly 20% of one person’s average annual water use. Water uses of 2,000 litres per day or more were regularly observed, especially during the summer.

Greywater and rainwater can help

Smart irrigation sensors, drought tolerant garden design and the use of alternative water sources (rainwater or greywater) can have a significant impact on the amount of mains water used. One of the monitored homes had a greywater system and a 2,000 litre rainwater tank, both for use in the garden. This home had the lowest overall water usage and the most vegetated garden of the whole study group. Some houses did not use any water for irrigation, whereas others used up to 60% of their total consumption outdoors.

Figure 1: Winter and summer water end uses of the 12 monitored homes.

Collecting rainwater and making use of greywater (the wastewater from the shower, bath and laundry) can substantially reduce mains water consumption and the amount of wastewater discharged from a property. Various systems are available, from simple to highly sophisticated. Even a drum placed under the downpipe as a rainwater collection tank can have an impact in supplementing mains water supply.

Improving efficiency could avoid restrictions

Short-term demand can exceed supply, especially during dry summer periods. The resulting water shortages can, in turn, lead to water restrictions imposed by the regional authorities. But are these water restrictions the only way to combat supply problems?

Many home appliances use more water than necessary. Toilets that use 12 litres per flush or more are not uncommon in New Zealand (30-litre cisterns still exist in some houses as well), yet water efficient toilets have been available for many years. Dual flush toilets using 3 or 6 litres should be standard in any home. Some modern ultra-low flush toilets can achieve even lower values. Considering each person flushes the toilet in their home around five times a day, using an average of 11,000 litres per person over a year, substantial water savings can be achieved.

High flow showers in some new houses

The average flow of shower heads in the study was 11 litres per minute (lpm), which is reasonably efficient. But flow rates of 18 lpm or more were also found. These higher flow rates are more common in new construction, with mains pressure hot water systems and pipework that can handle the higher flows. So, instead of moving forward in conserving resources, we are doing the opposite.

Low flow shower heads or flow restrictors can easily be installed, and a wide variety of models at varying prices are available. However, not all models might be compatible with your system. The pressure of the system can have a huge effect on overall performance and shower quality. On average within the study group, 0.7 showers were taken per person per day, with an average duration of 7.7 minutes in both summer and winter.

Changing your existing washing machine to a more efficient front loading machine could have a major impact on your water consumption. Some washing machines in the study used up to 180 litres of water per load. Highly efficient front loaders use just over 50 litres per load. It is more common now for washing machines to carry a water efficiency label, showing a star rating and a consumption value.

Fix leaks first

Before starting to change appliances, it makes sense to fix any leaks. In the first weeks of monitoring, the leak from one house represented 56% of its total usage, equivalent to 73,000 litres per year. This is more than an average person would use over this period.

The average leakage rate of the whole study group was between 3% and 4%, for summer and winter respectively. The most common leak was from the toilet cistern, followed by dripping taps. In some cases, changing a single seal could save thousands of litres.

Reduce water use

According to an old proverb, ‘You don’t know the worth of your water until the well runs dry’. Today a more accurate version might be, ‘You don’t know the worth of your water until you are being metered’. Without monitoring use, it is not possible to know how much is being consumed; there is also no baseline data to show the effectiveness of any conservation measures.

There are many opportunities to reduce the amount of water used in our houses, without having to change our behaviour drastically. It’s not about the lack of technology or the lack of water efficiency measures. It’s more about our slow take-up of these technologies to improve the sustainability of our buildings.

For more

This work was funded by Building Research. The final study report (SR159) is available for free download or purchase as a paper copy from the BRANZ bookshop, see www.branz.co.nz or phone 0800 80 80 85.

Download the PDF

More articles about these topics

Articles are correct at the time of publication but may have since become outdated.

Figure 1: Winter and summer water end uses of the 12 monitored homes.

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