How Often Should You Drain and Refill a Hot Tub? A Simple Formula and Step-by-Step Guide

Published November 4, 2026 · A Clear Alternative Water, Pennsauken NJ, since 1991

Most home hot tubs need to be drained and refilled every three to four months. For a closer number, use the industry rule of thumb: divide your tub's gallons by 3, then divide by the average number of people who use it each day. A 400-gallon tub used by two people a day works out to about 67 days, or a little over two months. Heavy use, cloudy water that will not clear, foam, or chemicals that will not stay balanced all mean it is time sooner. When you refill, fresh trucked water fills a hot tub in minutes instead of hours, which helps a lot in cold weather. A Clear Alternative delivers hot tub and pool water across eight South Jersey counties; call 856-856-5210 any time.

Why Hot Tub Water Wears Out

A hot tub holds a small amount of very warm water shared by several people. Every soak adds body oils, lotions, sweat and soap, and every dose of sanitizer, pH adjuster and shock adds dissolved solids that never leave the water. Over time, the total dissolved solids (TDS) build up until chemicals stop working well. The signs are familiar:

• Water stays cloudy even after shocking and cleaning the filter.
• Foam builds up when the jets run.
• pH and alkalinity swing and will not hold steady.
• Sanitizer gets used up quickly, or a chlorine smell lingers.
• Skin or eye irritation after soaking.
• A waterline ring that keeps coming back.

Once water reaches this point, more chemicals rarely fix it. Draining and refilling resets everything.

How to Work Out Your Drain Schedule

The formula is simple: gallons divided by 3, divided by average daily users, equals days between water changes. Ole's Pool and Spa and many other spa dealers use this same rule of thumb.

• 300-gallon tub, 2 users a day: about 50 days
• 400-gallon tub, 2 users a day: about 67 days
• 400-gallon tub, 4 users a day: about 33 days
• 500-gallon tub, 1 user a day: about 167 days, though most makers still suggest a change every three to four months

Count a user each time someone gets in. A family of four soaking on weekends averages fewer daily users than a couple who soaks every night. Sundance Spas recommends a full drain, clean and refill every three to four months for most home tubs used two to four times a week. Always check your owner's manual; some salt-water systems allow longer intervals.

Rental Properties and Heavy Use

Short-term rentals and shared tubs see many more users, often several a day, so the formula may call for a refill every few weeks. Many rental hosts drain between busy stretches. Keeping fresh water on a schedule is easier when the refill takes minutes.

How to Drain and Refill a Hot Tub

1. Flush the Lines Before Draining

Biofilm builds up inside the plumbing where you cannot see it. Add a spa line flush cleaner to the old water, run the jets for the time on the label, and skim off any foam or flakes that come up. Do this before draining, while there is still water to carry the cleaner through the pipes.

2. Turn Off the Power

Shut the tub off at the breaker so the pump and heater cannot run while the water is low.

3. Drain

Open the drain valve with a garden hose attached, or use a submersible pump for a faster drain. Send the water to an appropriate spot away from your foundation, and check your town's rules about where spa water may go.

4. Clean the Shell and Filter

Wipe the shell, waterline and jets with a non-foaming spa cleaner, then rinse well and remove the rinse water. Clean the filter cartridge or swap in a clean spare. Inspect and clean the cover while the tub is empty.

5. Refill Through the Filter Housing

Fill through the filter compartment, not straight into the footwell. Spa makers such as Jacuzzi say this pushes water through the plumbing first and helps prevent airlocks. Fill to the level your manual specifies, usually the middle of the skimmer opening.

6. Restore Power and Balance the Water

Turn the breaker back on, check that every pump runs and the jets flow, and add your start-up chemicals. Test and adjust pH and alkalinity, add sanitizer, and let the tub heat with the cover on before anyone uses it.

Balancing Fresh Water After a Refill

Fresh water is a clean start, but it still needs balancing before the first soak. Test it once the tub has circulated for a while, then adjust in this order:

1. Total alkalinity first, since it steadies pH.
2. pH next. Jacuzzi recommends a pH of 7.2 to 7.6 before first use.
3. Calcium hardness, following your tub maker's range. Very soft water can be hard on equipment, and very hard water leaves scale.
4. Sanitizer last, to the level your chlorine or bromine program calls for.

Add chemicals with the jets running and the air valves closed so they mix evenly, and give each one time to circulate before retesting. A tub that starts with balanced water usually stays easier to manage until the next drain.

Refilling a Hot Tub in Cold Weather

South Jersey winters are hot tub season, but they make refills harder. Outdoor spigots may be shut off for the winter, hoses freeze, and a slow hose fill can leave the tub sitting partly empty for hours in freezing weather. Spa guides warn against partially draining a tub and leaving it off in winter, because water left in the plumbing can freeze and crack pipes or equipment.

• Pick a milder day if you can, and plan the drain and refill for the same day.
• Get power back on quickly once the water covers the jets and reaches the fill line, so the heater and freeze protection can work.
• Keep the cover on as soon as the tub is full.
• Use a fast fill. Trucked water fills a typical tub in minutes, so the empty time is short.

If you are shutting the tub down for the winter instead, follow your manual's winterizing steps fully. A partly drained tub that is left off is the worst of both choices.

Why Use Trucked Water for a Hot Tub

Most hot tubs hold a few hundred gallons, so they do not need a full pool tanker. We run a small truck sized for hot tubs, spas and dunk tanks. A truck fill:

• Takes minutes instead of the hours a garden hose can need.
• Works when your outdoor spigot is off or your hose is frozen.
• Avoids filling from a well with iron or other minerals that can stain the shell and fight your chemicals. Our guide on filling a pool with well water explains the same issue for pools.

Our hot tub and spa water delivery page explains how a spa fill works. If you also have a pool, our guide to how many gallons your pool holds can help you plan a spring refill, and our pool closing guide covers winter care.

Serving Eight South Jersey Counties

We deliver hot tub, spa and pool water in Burlington, Camden, Gloucester, Atlantic, Salem, Cape May, Mercer and Monmouth counties. See our service areas for the towns we cover.

When to Call A Clear Alternative

Call us when your hot tub is due for a water change, when a hose fill is not practical in cold weather, or when you manage rental tubs that need regular refills. Tell us your tub's capacity and where the truck can park, and we will schedule the right-sized truck. A Clear Alternative is a family-run company that has served South Jersey since 1991 from 9230 Collins Ave in Pennsauken. Call 856-856-5210 any time, reach our office at 856-663-8088, or request a quote online.

Frequently Asked Questions

How often should I drain my hot tub?

Most home hot tubs need a drain and refill every three to four months. For a closer estimate, divide the tub's gallons by 3, then by the average number of daily users.

How long does a 400-gallon hot tub's water last?

About 67 days with two users a day, using the gallons divided by 3, divided by daily users rule of thumb. With four users a day, it is about 33 days.

Should I flush the lines before draining?

Yes. Add a spa line flush cleaner to the old water and run the jets before draining, so the cleaner can reach biofilm inside the plumbing.

Where should I put the hose when refilling a hot tub?

In the filter compartment, not the footwell. That pushes water through the plumbing first and helps prevent airlocks.

Can I refill a hot tub in winter?

Yes, but plan it so the tub is not left partly empty and off in freezing weather. A fast truck fill keeps the empty time short.

Do you deliver water for hot tubs?

Yes. We deliver hot tub and spa water with a small truck sized for spas in Burlington, Camden, Gloucester, Atlantic, Salem, Cape May, Mercer and Monmouth counties.