Water cremation is exactly what is sounds like on the tin. Just like the process of traditional flame cremation reduces the body to ashes using heat, water cremation does the same using hot water. Also known as alkaline hydrolysis, water cremation is relatively new to Aotearoa - in fact, it's currently only available in Christchurch - but has been used around the world for a number of years.
Here, you can explore how water cremation works, what makes it different to flame cremation (other than the obvious) and why some people are choosing it over more traditional options.
How does water cremation work?
Water cremation uses a combination of water, heat, pressure, and an alkaline solution to accelerate the natural process of decomposition. If a body were buried in-ground, it would take decades to fully decompose, but with water cremation it's slightly faster, taking on average only 4.5 hours!
- To begin, the deceased is wrapped in a natural, biodegradable shroud, often made out of wool. They are then placed inside a specialised stainless-steel vessel, some of which are known as 'Resomators'.
- Water and an alkaline solution (potassium hydroxide) is then added, and then vessel is pressurised and heated to 150°C. You might think this means you are 'boiling' someone, but this is a common misconception. Due to the high pressure, the water never reaches boiling point.
- Over several hours, the soft tissues break down into their basic organic components, leaving a DNA-free combination of sugars, amino acids, and soap that can be returned to the local water system.
- At the end of the process, only the bones and medical implants (like artificial joints, dental fillings, or pacemakers) are left. Anything metal is sterilised and recycled, while the remaining bones are dried, processed, and returned to the family in the form of white ash.
- People can choose to be cremated using water, regardless of how they died. The only current limitation is that you need to weigh less than 150kgs.
What makes water cremation different to flame cremation?
| Water Cremation | Flame Cremation |
| Uses water, heat (150°C) pressure, and alkali | Uses high-temperature combustion (850°C-1100°C) |
| Does not involve combustion | Produces emissions through burning |
| Leaves behind bones, that are processed into white ashes. Typically you get 20-30% more ashes than with flame cremation | Leaves behind bones, which are processed into grey ashes |
| No casket needed, only a biodegradable shroud | Wooden or cardboard casket required |
| Pacemakers can be left in the body | Pacemakers must be removed due to explosion risk from high temperatures |
| Environmentally friendly | Not as environmentally friendly |
Why might people choose water cremation?
- If you're eco-friendly and care deeply for the planet, then water cremation is a good option to help keep your environmental footprint small. It uses 90% less energy consumption than flame cremation, and involves no burning with fossil fuels - it can be run using solar power! Approximately 242kgs of CO2 is released into the atmosphere with flame cremation, along with harmful chemicals like mercury if the deceased had dental fillings. With water cremation, that drops to 0kg, with no other harmful chemicals being produced as a by-product.
- Water cremation is slightly cheaper than flame cremation, mainly because a casket is not required.
- Water cremation is more 'gentle' than flame cremation, and it's a process that you can be closely involved in if you wish. You are able to be in the room to say your final goodbyes, and even help wrap them in the shroud and place them in the machine. With flame cremation, this would be too dangerous as the temperatures are too high.
Updated: 31 Jul 2026