But most of the top-watering of plants and lawns is likely to do more harm than good, according to one plant expert.

On average, daily water consumption in 2013 was about 130 megalitres but as the temperature rose to 34 degrees in December the ACT recorded its highest water consumption for the year with 224 megalitres used on December 23.

Adjunct professor of landscape architecture at the University of Canberra Dianne Firth said residents were wasting water.

''People are not used to just watering their gardens, they are splashing it around … the humidity really drops and it's dry, so when you use a sprinkler it feels better, but it's really bad for the garden because it doesn't water,'' Dr Firth said.

''For non-vegetables, ornamental gardens and lawns, once a week is more than enough if it's slow deep watering. Put it on in the evenings and then test how deep it's gone down - 10 centimetres means you won't have to water again for at least a week, maybe two weeks. And if the garden beds are well mulched, that sort of water can do for a month.''

Dr Firth said the coming heat wave should not change watering patterns for lawns or ornamental gardens if done correctly.

The Bureau of Meteorology was forecasting temperatures would reach 34 degrees on Sunday and 33 degrees on Monday.

Maximum temperatures were then expected to soar to 37 degrees on Tuesday and 39 degrees on Wednesday. The bureau is then predicting a shower or two to develop, but the rain will bring little relief, with a top of 38 degrees on Thursday and Friday.

Permanent water restriction measures mean lawns and plants in the ACT can be watered using a hand-held hose fitted with a trigger nozzle, a bucket or a watering can at any time, but sprinklers and other irrigation systems may only be used to water lawns and plants before 9am or after 6pm.

When watering either by hand or hose, lawns and plants may only be watered without causing pooling or run-off.