How Long Does it Take to Fill a Reverse Osmosis Tank?

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Reverse osmosis systems come with a storage tank for convenience. Thanks to the tank, filtered water is delivered fast and at high pressure.

Without a storage tank, it would take you 5 to 10 minutes to get a glass of clean water from an RO unit.

But how long does it take to fill an RO tank? It takes about 2 to 4 hours to fill a reverse osmosis tank. The RO water filtration process is quite extensive and, thus, takes more time to complete.

What is a Reverse Osmosis Storage Tank?

An RO storage tank is a pressure tank that collects the water purified by the RO membrane. The tanks come in different capacities depending on the volume they can hold.

Since reverse osmosis water filtration is a slow process, pushing water across the semi-permeable membrane takes some time.

The RO tank accumulates the clean, filtered water for immediate access.

What is the Fill Rate of a Reverse Osmosis Tank?

The fill rate is the time it takes to fill an RO tank with clean water. The fill rate varies depending on the following factors:

Type of the RO system

There are different types of RO systems on the market today. These systems vary in price and output capabilities.

Additionally, these reverse osmosis systems produce different gallons of water daily. It could be 50, 70 or 100 gallons.

As such, these systems will fill their storage tanks at different rates. The more gallons a unit produces daily, the faster it will fill the tank.

Water pressure

The incoming water pressure greatly impacts how quickly a reverse osmosis storage tank fills. An RO system can work within 40-80 psi, but the most efficient water pressure is around 60 psi.

Note that the lower the water pressure, the less efficient the RO system will be and the longer it will take to fill the tank.

If your system has very low pressure, you can add a pump to your plumbing to boost it.

Excessive water pressure (above 80 psi) can cause some RO systems to malfunction. Therefore, if the water pressure going to your unit exceeds 80 psi, use an RO pressure regulator to maintain it.

Condition of the RO filters and membrane

New reverse osmosis water filters allow faster water flow than older ones. A filter that is only a month old works more efficiently than one that has been in use for more than a year.

The older the RO filter, the longer it will take to fill the storage tank.

Since the filters can make your RO tank fill slower than average, you need to change your system’s filters every 3 to 6 months, depending on the filter.

Always check on the recommended timeframe on the filter or membrane to prevent clogging, as this can slow down the tank’s fill rate.

Why is My RO Storage Tank Not Filling Up?

If your reverse osmosis tank is not filling up, chances are, your faucets are not getting enough water. You need to troubleshoot the RO system for the best results.

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Dr. Peter Gleick

Dr. Peter Gleick is an experienced water filtration engineer and technical writer for He is an expert in water purification and filtration, focusing on helping people get clean, safe, and healthy water for domestic use. He has more than 10 years of writing experience and has numerously contributed to leading publications in this field.

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