Stainless steel tanks and poly tanks are popular nowadays. After all, both are great rainwater storage options. Unfortunately, this popularity might be behind the confusion during the selection process. If you’re one of those who still do not know which type of tank to purchase, here’s a short, but comprehensive guide to poly and stainless steel tanks.

Before comparing between stainless steel and poly tanks, it’s a must to remember that stainless steel is graded. A grade is usually represented by a series of numerals. For example, the stainless steel used for kitchen sinks is graded 304, while the stainless steel intended for use in a marine environment is graded 316.

What makes stainless steel what it is is an element called Chromium. To make stainless steel resistant to corrosion that harsh acids and salty sea water can cause, Molybdenum is also added. Molybdenum is present in 316 stainless steel, which is used in implants and surgical instruments.

The type of stainless steel used to create a rainwater storage tank has a grade of 304 or lower, unless it’s in close proximity to the ocean, then 316 grade will be used.

The Differences


Every tank needs to be capable of staying upright. To make that possible, a round poly tank may be set on crusher dust, while a stainless steel tank must be set on a solid and compact foundation.

It’s important to set the metal tank on a solid foundation because of its construction. It is heavy, and a fall can instantly compromise its structural integrity.


Both poly and stainless steel tanks can last several decades.

The material used to create plastic tanks is capable of withstanding the heat and light from the sun. The sun’s heat and light can cause most other types of plastic to become brittle.

As mentioned above, stainless steel tanks have Chromium, which helps prevent rusting. But since the said element cannot prevent dirt from sticking to the tank, you should still make it a point to clean steel tanks every so often with fresh water and a clean piece of cloth. It is also important to keep solvents away from them, and that they be welded properly. Incorrect welding neutralises the protective part of the steel tank, and when this happens, rust and corrosion will occur.


Different stainless steel tank models have different warranties, but high-quality metal tanks should have warranty proportional to how it’s made. Most steel tanks have thirty-year warranties since they are designed to be durable.

As for the plastic tanks, they have a 25-year warranty, although they can last more than 25 years.


Both poly tanks and stainless steel tanks do not require much in the way of maintenance or upkeep. A first flush diverter on each downpipe can help to keep the rainwater pure. The strainer at the tank’s inlet helps to filter the water, so it must be cleaned out 2 or three times a year, depending on the amount of leaves and dust on your property. Post tank filtration is also a good option for drinking water, or water used for cooking or showering.

Most large tanks, if installed and maintained correctly, will not need to be completely cleaned out for 5-10 years.

Water Quality

Both stainless steel and poly tanks can store clean water, and both are made from food-grade materials suitable for storing drinking water. Both must also be installed according to the manufacturer’s instructions. To ensure your water remains as clean as possible, it’s best to install the tank as soon as it arrives on site, placing it on its intended base and connecting it to the catchment system via pipes.

Stainless steel tanks are a great option for storing drinking water, but they are much more costly than poly.


Both poly and stainless steel tanks are capable of resisting physical impact. Also, they neither warp nor bulge.

Our polyethylene and stainless steel tanks are amazing options for rainwater collection and storage. So if you don’t have a tank already, check out our collection now!