26 October 2022

What are the Best Colour Tanks for Keeping Water Cool?

So, you’re looking at purchasing a rainwater storage tank, but you’re not sure what colour you should opt for? You want to maintain an even temperature inside the tank all year round, and you’ve got a hunch that some colours are going to be better than others when it comes to keeping the water cool...

Water Tanks

Joint rainwater tanks

You’re right: there are some poly colours that are better than others for maintaining an even water temperature inside your rainwater tank. And depending on what you are using your tank water for, this could be an important factor when it comes time to purchase.

Today we’re going to have a quick look at why you need to maintain a stable water temperature inside your tank, the best color options to achieve this, and a few other tips on how to make sure that your tank water stays as cool as possible, even when the mercury soars.

Why Should I Keep my Tank Water as Cool as Possible?

If you’re using your rainwater for human or animal consumption, we recommend that you keep it as cool as possible, all year round. Warm water is more likely to encourage algae bloom or become a breeding ground for harmful bacteria or other nasty contaminants.

When the pocket of air between the water and the roof of the tank heats up, it creates an atmosphere conducive to the growth of mildew and slime, which can be a problem even if your water is not being used for drinking.

What Colour Tank is Best for Keeping Rainwater Cool?

As the sun beats down on your water tank, it’s going to warm the poly and this heat will be transferred, slowly warming the air and water inside. It’s not a quick process, but it is guaranteed to happen, and even the difference of a degree or two might be enough to cause issues.

So, the burning question of today’s blog: does the poly colour you choose affect the temperature of the water inside?


It’s not too difficult to understand: dark colours absorb heat quickly, while light colours reflect it. So, the darker your tank, the quicker it will warm up and begin transferring heat to the water inside.

We recommend the following colours as our top #5 picks for ensuring that your water remains as cool as possible, even on a warm summer day:

  • Surfmist (Off White)
  • Evening Haze
  • Dune
  • Smooth Cream
  • Gull Grey

Will My Water Tank Cool Down at Night?

Yes. In Tasmania we rarely experience hot nights, so you can count on your water tank and its contents cooling down after the sun goes down.

Compare this to the climate in Central Australia, where the average daytime temperature in summer is about 35°C and night times are a minimum of 20°C - in these temperatures, keeping tank water cool can be a real problem.

Windspray 11250 litre Poly DOVER

Will the Size of my Tank Affect How much it Heats Up?

Yes. Again, this isn’t rocket science: the greater the volume of water inside the tank, the longer it will take to heat and the less of a threat it poses.

Full tanks of 4500L or over will experience very little if any change of water temperature, regardless of the weather.

Smaller domestic tanks are more likely to experience fluctuations in temperature, especially if they aren’t full, are positioned in direct sunlight or against a northerly-facing brick wall or other solid structure which will absorb heat.

What Else Can I do to Stop my Tank Water Heating Up?

If you’re concerned about the water heating up inside your tank, think carefully about where you position it.

If possible, avoid placing it against a solid brick wall, or a northerly-facing wall. Brick walls continue to radiate heat long after the sun goes off them, and this won’t assist in allowing the water to cool naturally inside the tank at night.

Avoid placing your tank in a position where it will get direct sunlight all day. You might have to be a bit creative - think of unused spaces under verandahs or decks, behind a timber screen or against a fence on the south side of the house.

Can I get Rid of Algae in my Tank?

If algae has bloomed inside your tank, don’t panic. Yes, it’s a nuisance, and it could pose a health risk if you are storing the water for human or animal consumption, but there are two ways of dealing with this issue:

1. Empty the tank completely, scrub it and flush it out


2. Use a chemical sanitizer to kill the algae in the water

If you aren’t keen on draining your tank, the second option is an easy, effective and reliable method of ensuring that your rainwater is safe to drink. Water purifying tablets are readily available online or from your local plumbing and tank accessory supplier.

Crm S lines 3

Will Water Heat up Quicker Inside a Galvanized Water Tank?

In theory, steel transfers heat faster than poly, however, galvanized steel has certain properties which reflect heat and therefore slow the transfer. To put it simply, yes, water inside a steel tank may heat faster, but it will also cool faster at night.

Again, when the volume of water is 4500L or above, the heat gained inside the tank is negligible.

Want to know more about what colour tank would be best for you? Contact us here or call us on 1800 752 784 and chat with one of our sales team.