Key takeaways

A home RO system is generally installed under the sink and connected to the cold water supply and the drain. Its proper operation depends in particular on pressure and the condition of the pre-filters and membrane. Maintenance must be tailored to the model, water quality, and the volume actually treated.

Where should you install an RO system?

Most home RO systems are installed under the sink, near the cold water supply, drain, and dispensing faucet.

Some compact models can also be installed on a countertop, depending on their design.

The goal is to minimize unnecessary tubing lengths to maintain good performance and make maintenance easier.

How much space should you allow?

The space you need depends greatly on the type of RO system.

For a tank-based model, you need to allow for:

• space for the filtration unit;
• space for the tank;
• clearance to replace the filters;
• access to fittings and tubing.

A direct-flow RO system can be more compact, since it generally does not require a tank.

To compare the two configurations: direct flow or a tank?

What tools do you need to install an RO system?

Depending on the model and your installation, you may need a few common tools:

• an adjustable wrench or open-end wrenches;
• tongue-and-groove pliers;
• a screwdriver;
• a utility knife or tubing cutter;
• a drill if a dedicated faucet needs to be installed;
• drill bits suited to the sink or countertop material.

Before starting any work, shut off the water supply and follow the user manual for your specific model.

Do you need to drill into the sink?

If the installation includes a dedicated faucet, you may need to drill into the sink or countertop.

Use a drill bit suited to the material: stainless steel, resin, wood, stone, or another surface.

Before drilling:

• check that there are no pipes or other components underneath;
• mark the location precisely;
• use the diameter required for the faucet;
• do not use hammer mode on a fragile surface.

If you are unsure, you can have a professional handle this step.

See also: how to install an RO water faucet .

How do you connect the water supply?

A home RO system is generally connected to the cold water supply.

The connection uses a fitting suited to the plumbing diameter and a dedicated supply valve.

The main steps are generally:

1. shut off the water;
2. install the supply fitting;
3. connect the tubing to the RO system;
4. check for leaks;
5. gradually restore water pressure.

Also see: how to connect the water supply tubing .

What pressure does an RO system need?

Pressure plays an important role in the operation of a reverse osmosis membrane.

Pressure that is too low can:

• reduce the production flow rate;
• increase the amount of drain water;
• reduce overall performance.

Conversely, pressure that is too high can exceed the manufacturer's specified limits.

You should therefore always refer to the recommended pressure range for your particular model.

What is a booster pump used for?

A booster pump increases the pressure applied to the membrane when the water supply pressure is insufficient.

It can improve:

• the production flow rate;
• the system's overall efficiency;
• operating stability.

However, its usefulness depends on the RO system model and the available pressure.

When should you replace an RO system's filters?

There is no single replacement interval for all RO systems.

The service life of consumables depends in particular on:

• the quality of the incoming water;
• the volume used;
• the type of filter;
• the unit model;
• the manufacturer's recommendations.

For a dedicated guide: how to maintain your RO system .

How do you know if the membrane is still working properly?

A membrane should not be replaced solely because a fixed period has elapsed.

You can monitor several indicators:

• an increase in output TDS;
• a decrease in the retention rate;
• an unusually low flow rate;
• changes in performance over time.

Monitoring TDS is particularly useful when you compare water readings before and after reverse osmosis.

What is a TDS meter used for?

A TDS meter enables you to estimate the total amount of dissolved ionic substances in water.

With an RO system, it is particularly useful for comparing:

• the TDS of the incoming water;
• the TDS of the water produced.

This comparison enables you to monitor the membrane's overall effectiveness.

To understand how it works: everything you need to know about TDS .

Caution: a single TDS threshold is not enough

A TDS reading alone does not tell you whether water is “pure” or “impure.” TDS is mainly used to monitor the total amount of dissolved substances and membrane performance.

How much water does an RO system send to the drain?

Not all RO systems have the same efficiency.

The amount of drain water depends in particular on:

• pressure;
• temperature;
• the membrane;
• the system's design;
• the water's mineral content.

It is better to consult the data for your particular model rather than use a single ratio for all units.

See also: RO systems with low water waste .

What does GPD mean on a membrane?

GPD stands for Gallons Per Day, meaning gallons per day.

This unit indicates a membrane's theoretical production capacity under given conditions.

One US gallon is approximately 3.785 liters.

For example, a 100 GPD membrane has a theoretical capacity of approximately 378 liters per day.

In practice, actual production depends on pressure, temperature, and water quality.

What membrane capacity should you choose?

A higher capacity generally enables faster production, but the right choice depends on the complete system.

In particular, you need to check:

• compatibility with the RO system;
• the flow restrictor;
• the pump, if present;
• the flow rate you actually need;
• the manufacturer's recommendations.

A larger membrane is therefore not automatically better for every installation.

Looking for an RO system suited to your installation?

Compare models by flow rate, pressure, membrane type, space requirements, and maintenance.

Frequently asked questions about installing and maintaining an RO system

Can you install an RO system yourself?

Many home models are designed for you to install yourself with a few common tools. However, the difficulty depends on the model and your existing plumbing.

How long does it take to install an RO system?

The time varies depending on the model, plumbing accessibility, and whether drilling is needed to install a dedicated faucet.

Do you always need a booster pump?

No. It is mainly useful when the available pressure is insufficient for optimal membrane operation.

How do you know when to replace the filters?

You need to follow the manufacturer's recommendations and take into account the volume treated, water quality, and changes in flow rate.

How do you know if the membrane is worn out?

A sustained rise in output TDS or a decrease in the retention rate may indicate a decline in performance.

Should TDS be below 50 ppm?

There is no universal threshold that alone allows you to assess water quality. TDS should primarily be compared between the RO system's inlet and outlet.

What does 75 GPD or 100 GPD mean?

This is the membrane's theoretical daily production capacity. A 100 GPD membrane corresponds to approximately 378 liters per day under the specified test conditions.

Further reading

• Understanding reverse osmosis
• Maintaining your RO system
• Understanding TDS
• Choosing your RO system

About this guide

This content is written by the Josmose team based on our experience with reverse osmosis systems and routine installation and maintenance procedures.

Josmose sells RO systems, filters, membranes, and accessories available through this page.