How we use it
Roughly 60 percent of all the water that we supply is used at home; however we can’t be exact because very few homes within the greater Wellington region have a water meter.
A recent Auckland study¹ found showers (34%), washing machines (23%), and toilets (18%) accounting for most household water use during winter, while in summer these three were joined by ‘Outdoor’ water use (18%) as the main household uses of water. Christchurch similarly identifies the bathroom, toilets, laundry and gardens as the main uses of water in households.
The amount of water used in the greater Wellington area isn’t constant: it varies, particularly by time of day and by time of year. The graph below shows ‘weekday’ water use patterns (average litres per second reservoir outflow rate, Monday to Friday) for summer and winter weeks during 2008, for a reservoir that serves a suburb where the vast majority of water connections are to households and there are no major commercial users. The light green line represents a summer day with high demand for water, the blue line a fairly typical winter day, with relatively low demand.
¹ Water Use in Auckland Households (EC1356), BRANZ, October 2008
Water use by time of day
Water use is higher in summer than in winter. For both seasons it is lowest between midnight and about 6am and higher around breakfast and dinner times, when people are showering, preparing meals, washing dishes and, in summer, watering gardens. The main difference between summer and winter days is seen between late afternoon and about 10pm. While water use in mid summer peaks in the evening, in winter the daily peak is around breakfast time.
The summer evening peak rate of water use shown for this suburb is more than double that for the winter evening and equates to each resident using almost 40 litres per hour (a little less than a half full bath). Garden watering is the main reason for higher summer demand. On a hot, sunny summer’s day, water use across our entire supply area can be 50 percent more than on a winter day.
Demand for water tends to be highest between December and March each year. How much water will be used is harder to predict at that time of year because of the huge effect that a dry summer and the resulting increase in watering can have on peak water use.
We aim to supply all but the most extreme peaks in water use, so water use during dry summer conditions is an important factor in deciding when to develop new supply capacity. Because of this, we concentrate our water conservation activity during summer.