Access to clean drinking water is something most New Zealand households take for granted. Municipal water supplies are treated and monitored to meet national drinking water standards, while many rural homes rely on rainwater tanks or private groundwater sources.

At the same time, interest in home water filtration has grown steadily. Many households explore filtration systems to improve the taste, clarity, or composition of their drinking water.

Among the different filtration technologies available, reverse osmosis systems are widely considered one of the most comprehensive methods for treating drinking water. These systems are used around the world in both residential and commercial applications.

This guide explains how reverse osmosis filtration works, what it can remove from drinking water, and when households in New Zealand may consider using this type of system.

Another common membrane filtration technology used in home water systems is ultrafiltration.

Ultrafiltration membranes are designed to remove particles and microorganisms from water. They are commonly used to filter:

• bacteria
• protozoa
• cysts
• microscopic particles
  

Ultrafiltration systems are often used for rainwater tank systems or rural water supplies, where microbial protection is important.

However, ultrafiltration membranes typically do not remove dissolved minerals or salts.

Reverse osmosis membranes are much finer than ultrafiltration membranes and are designed specifically to remove dissolved contaminants such as nitrates and fluoride.

Because of these differences, the two technologies are often used for different water conditions.

Because reverse osmosis membranes remove many dissolved substances, they can also reduce naturally occurring minerals that are present in water.

This can sometimes make RO-filtered water taste very neutral or “soft”.

To address this, many modern reverse osmosis systems include a mineral restoration stage after filtration.

Mineral cartridges may use natural mineral media to reintroduce small amounts of beneficial trace minerals into the purified water. This stage can improve the taste and balance of the water while maintaining the benefits of reverse osmosis purification.

For example, mineral cartridges such as the Alka Spring stage are designed to enrich purified water with trace elements and support a more balanced mineral profile.

Reverse osmosis systems are commonly installed as under-bench drinking water systems connected to a dedicated kitchen tap.

Households may consider reverse osmosis filtration when they want to reduce:

• nitrates in groundwater
• fluoride in municipal water supplies
• heavy metals or dissolved contaminants
• elevated total dissolved solids
  

Because RO membranes are extremely fine, these systems are typically used specifically for drinking and cooking water, rather than for whole-house filtration.

Many homes combine multiple filtration approaches. For example, a whole-house filtration system may treat water entering the home, while a reverse osmosis system provides additional purification at the kitchen sink.