How Long Can You Store Water in a Tank?

storing water in a tank

Even though water doesn’t technically expire, there is a limit to how long you can keep it in your holding tank before it starts to smell or taste stale. Bottled water in an airtight container can stay fit for consumption for ages. It is the storage tank holding your rainwater, well water, or municipal supply that you should be worried about.

With the right purification and storage equipment, you can have your water fit for human consumption for more than a year.  Filtered, treated, and frequently circulated water won’t start growing microbes and algae that bring the smell. Still untreated water will start smelling and deteriorating within 2 weeks.

Water doesn’t go bad. It gets contaminated or grows microbes and other organics

It Depends on How You Want to Use the Water

How long you hold water in your off grid tanks depends on how you want to use it. Irrigation water can lie in a pond for as long as you want. The only problem will be the mosquitoes.

However, if you want to use the water for laundry, cleaning, cooking, drinking, or dishes, you should impose some virtual expiry date to avoid the risks of using contaminated water.

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Keep Your Water Moving

Agitating your water or running through the entire reservoir every now and then reduces the risk of long-term contamination. If you keep using your water, chances are you will have to replace it long before you have to worry about the smell, algae growth, and the development of other forms of bacteria.

Avoid hoarding rainwater thinking that you will use it when drought strikes – unless you want to use it for irrigation. Using the rainwater as soon as possible and holding off the alternative for dry time use would be a better idea.

Build a System with Two Distinct Holding Tanks

Another good way to keep the water flowing through your faucets fresh is by ensuring that you have two distinct tanks in your system. The first tank should hold freshwater that hasn’t gone through your entire filtration system while the second is for fully purified water that will then flow to your taps.

ProTip: Pre-treating your water with chlorine long before it lands into any tank is a good way to discourage bacteria and algae growth. Mix non-scented NSF-approved household bleach (5.25% chlorine) in the reservoir at the ratio of 1 gallon of bleach for every 1,000 gallons

This is opulent and unnecessary for small storages since chances are you will be refilling your tank long before its time to start worrying about ‘stale water.’

The dual-storage option is a good idea for people who rely on rain or river water throughout the year. A huge and preferably underground tank will help you survive the dry seasons of the year and the winter months.

Shock Treat Your Well Every Now and Then

If you use a partially open well as your primary water source, there is the possibility that some bacteria, insects or small animals end up in the well and contaminate the water giving it a smell.

Start by sealing the well completely and installing an electric or manual pump to avoid future contamination.

After this, you can shock treat the well to kill existing bacteria and contaminants. Shock treatment involves adding a good proportion of chlorine into the well, letting it sit for up to five hours before pumping and disposing of all the water until you can no longer detect the smell of chlorine.

  • Open the well head to gain direct access to the well
  • Pour in the chlorine
  • Grab a beer (or coffee) and wait for 6 hours
  • Reattach the well pump but disconnect its outlet from supplying your holding tank
  • Run the pump until you can no longer smell chlorine in the water. This can sometimes take up to a day to accomplish

You can check out this guide to well shocking that the University of Nevada prepared. It is more detailed and tells you exactly how to do it right.

Ensure You Use Clean Food Grade Tanks

Treating and filtering your water will do you no good if you still store it in dirty open containers. Keeping your tank clean and sealed will let you store freshwater for longer.

Clean your tanks at least twice a year(or just before the rainy season if you harvest rainwater). Cleaning gets rid of trace amounts of algae or even sediments that would otherwise encourage bacteria growth or algae infestation.

Keeping a nice seal on the tank keeps bugs and mosquitoes from setting up shop in your water. This is the first step to keeping your reserves clean for longer. It also saves you the trouble of fighting tons of mosquitoes every time the sun goes down.

The seal doesn’t have to be air-tight. It just has to be good enough not to make the water inside obvious and perfect enough to keep twigs, bird poop, and leaves from falling in.

A seal on an underground or ground-level tank will also keep small rodents from falling into the tank.

A good water tank will be made of:

  • Properly treated concrete
  • Wood or aluminum sealed with a food grade plastic sheath
  • Food grade plastic
  • Stainless Steel

Always filter stored water before using it to get rid of any debris, algae, or other biomass that grew during storage.

Why Does Stored Water Taste Weird?

Even uncontaminated water that has sat in storage for months will taste different. The flat and unwelcoming taste is almost similar to the water you get from freshly boiled water. This is because there is not much oxygen (air molecules) in the water. Agitating the water will aerate it and restore that natural refreshing ‘taste’ we’re all used to.

Should I Rotate My Stored Water Each Year?

Not really. Pre-treated water stored and firmly sealed tanks will stay usable for years. Actually, a pre-treated 55 gallons drum with the cap tightly screwed on can hold water for even five years without a problem.

The general advice to rotate your stored water at least once a year is just a failsafe to ensure that you don’t consume contaminated water just because your storage tank or the water wasn’t as sterile as you thought when starting the storage.

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Bottom Line

Very few people have to worry about how long they can store their water in an off grid setting. Chances are you will be pumping in or bringing in freshwater for human consumption on a weekly basis.

However, if you want to fill up your underground tank for winter or get the very best out of your rainwater, don’t cut any corners when it comes to purifying, treating, and storing your water. A few bacteria, debris, or algae can grow into a serious problem over a couple of months.