It’s a well-rehearsed debate – hot water or cold water when washing your laundry?

Those who swear by hot water will strike home the point that heat kills bacteria, and therefore gives a more effective wash.

On the other side, we have the cold water spokespeople, whose main argument is that hot water not only shrinks your clothes but also drowns your power bill with the energy needed to heat the water.

So what temperature should we actually be washing our laundry in? Colorado-based care expert Steve Boorstein told Real Simple: “Technological advances in both machines and detergents, and not just cold specific detergents, have made cold washing a highly effective option.”

Energywise says washing on a warm cycle can use up to 10 times as much energy as a cold wash, which is an extra 20 to 40 cents for every single wash.

Protein stains, such as sweat or blood, can set in when washed in hot water, Boorstein says. But some dry-fit workout clothes tend to still smell after a cold wash cycle, which is when Boorstein suggests giving them a cold wash pre-rinse within 20 minutes of a workout before putting them through a warm wash.

Washing on a warm cycle can use up to 10 times as much energy as a cold wash. Photo: Tessa Chrisp

Consumer Reports says “don’t bother” with hot water. Consumer tests over the past 15 years have found front loaders’ and high-efficiency top loaders’ warm wash cycles have declined by 15 degrees, and detergents have adjusted accordingly.

Persil NZ suggests there are three forms of energy needed for the right balance to effectively remove soil from fabric: thermal energy, gained from hot or warm water; mechanical energy, from the machine’s action; and chemical energy, supplied from the detergent used.

In general, the company says although all detergents can be used in cold, warm or hot water, the effectiveness of the detergent will decrease as the water temperature decreases.

Optimal temperature should be decided through a number of factors, including the amount of dirt, type of fabric and the likelihood of colour running, all of which will be outlined and given a temperature recommendation on the care label.

– stuff.co.nz