How to Add Water to a Hot Tub (Tips to Avoid Contamination)

Jennifer Rhodes

By Jennifer Rhodes · Updated

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Adding the water is an exciting step when you first set up your hot tub. But is there anything you need to know before just filling it up?

For the most part, it's super easy to put water in a hot tub. All you need to do is hook up the hose, place the end into your spa's filter well to ensure the new water is filtered on the way in, turn on the spigot, and watch your spa fill up.

However, there are also some things to watch out for, like water cleanliness, the condition of the hose, and what to do in winter.

Whether you have a hot tub already, or just want to get all your ducks in a row before buying your first spa, here's everything you need to know about adding water to a hot tub.

Is tap water okay for a hot tub?

In general, yes. Can you imagine how much more expensive a hot tub would be if you had to add special water to it? Thank goodness you can just hook up your hose, pop it into the filter well, and turn it on.

However, you do have to be a little careful in some cases. For one thing, not all garden hoses are clean. If your hose has been sitting around with standing water in it, then you should flush it thoroughly or replace it with a new hose to make sure that you're not filling your spa with dirty water to start with.

To flush a hose, just run fresh water through it for a few minutes before filling your spa. If you've just used it to rinse out the spa during cleaning, you've probably just flushed it already. Alternatively, you could water the plants.

You can also use a pre-filter to ensure less chance of sediment entering your hot tub from the garden hose. This is a simple device that attaches to the hose and filters out any large particles before they can enter your hot tub:

Guardian Max Clear PRO Hot Tub Garden Hose Carbon Pre Filter
Guardian Max Clear PRO Hot Tub Garden Hose Carbon Pre Filter
View on Amazon

Some homeowners actually keep a separate hose just for their hot tub. This way you can keep it inside and not risk it getting left to fester after being used for other things around the yard.

Can you fill a hot tub with soft water?

Hot tubs can be filled with soft water. Soft water is actually easier to manage in some ways when it comes to hot tubs, as it can help to prevent mineral buildup and prolong the life of the equipment.

That said, in areas with very soft water, you will need to add a calcium hardness increaser to balance the water. The recommended calcium hardness level in a hot tub is between 150 and 250 ppm (parts per million).

If the calcium hardness is too low, it can cause corrosion of the hot tub's equipment. On the other hand, if the calcium hardness is too high, it can lead to scale buildup—which can also damage equipment and negatively affect the hot tub's performance over time.

Can you put too much water in a hot tub?

Yes, you can overfill a hot tub. As a general rule, you want to leave six to eight inches of space available between the top of the tub and the surface of the water. This is because you have to account for the fact that the water level will rise when people get in.

If you ever get in and it overflows over the sides, then you put too much water in. For some models, overfilling is no big deal, but for others, it can bend or warp the shell, damaging your hot tub or even voiding the warranty in some cases.

It's better to be safe than sorry when it comes to the water level in your hot tub.

How do you add water to a hot tub in winter?

For the most part, filling a hot tub in winter is much the same as at any other time of year. However, there are a few additional things you'll need to be aware of—mostly to do with the water source, and not the spa itself.

If you live in a cold climate and need to refill your spa during winter, you could get a nasty surprise when you go to fill up and find your hose has frozen solid.

Luckily, you can avoid this problem if you just do a couple of things to prepare ahead of time:

  • When it starts getting cold as winter approaches, roll up your hose and take it inside the house. This way, the hose won't freeze and will be usable when you need it.
  • You may also need to thaw the outside spigot with a little hot water before you attach the hose. Then, once water starts coming out the tap, simply hook up your hose and fill your hot tub as usual.

As long as you have running water, you can fill your spa without problems. Just be sure to keep the lid on while it's heating though; otherwise it will have to work extra hard to get up to temperature in freezing weather.

How often do you need to 'top off' your spa water?

This all depends on how much water you lose during regular use. The more you splash around, causing water to go over the sides, the more you'll need to top it up. (Ever seen kids use a spa?)

The most important rule here though is never let the water level fall below the highest set of jets. This can cause mechanical issues by letting air into the lines or equipment, which is known as an air lock.

If you ever miscalculate the chemicals, you can always top off with some fresh water to reset the water balance, or decrease the concentration of the sanitizer if it's reading too high. This is a quicker method than waiting for the levels to reset themselves.

If you leave the cover off for long periods of time, you'll also need to refill it more often as your spa can lose a lot of water through evaporation. This is one reason why it's important to keep the cover on when you're not using the spa.

How many buckets does it take to fill a hot tub?

If you don't have a hose nearby, you might be wondering how long it will take to fill your hot tub by lugging a bucket back and forth from your house.

While this can work for topping up the spa with small amounts, it's time to think about purchasing a hose as it's impractical to fill a whole spa this way—it would simply take too long.

If you're still determined to do it with buckets, you first need to know how many gallons your spa contains. Divide that number by the size of your bucket in gallons. The result is how many bucketfuls you will need.

For example, you might have a spa that holds 500 gallons. If you use a five-gallon bucket, 500 divided by 5 is 100, so this would take you 100 full trips with the bucket to fill up.

Getting a hose is sounding pretty good now, right?

The optimal outdoor setup for hot tub maintenance

Having a hot tub in your yard can turn into a tedious task every time you need to drain and refill it if you don't have the right setup:

  • Ideally you want an outdoor water source close by for filling and top-ups. You do not want to carry buckets of water from the house since that is going to be a lot of work. If you don't already have an outdoor spigot, you'll need a plumber to install one, but it will be so worth it.
  • Another critical factor in optimal hot tub set up is a good quality hose—long enough to reach from your water source to the tub. Instead of your old garden hose that lays around in the yard, having a separate one just for your tub can save you a lot of headache and hassle when it comes to keeping your spa water fresh and clean.

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