How Often Should You Drain Your Hot Tub?

Quick answerEvery 3–4 months for typical use. Or calculate it: tub gallons ÷ 3 ÷ daily bathers = days between drains. A 400-gallon tub with 2 daily users needs fresh water about every 66 days. If chemicals stop behaving — sanitizer vanishes, foam returns instantly, water never quite clears — the water is saturated and no chemical will fix it.

Why water "wears out"

Every dose of every chemical leaves dissolved solids behind. Sweat, oils, and minerals add more. Total dissolved solids (TDS) only ever goes up, and past a threshold the water gets chemically stubborn: sanitizer is consumed instantly, pH swings, foam and haze return within days of treatment. That's not a chemical problem — it's saturation, and drainage is the only cure.

Signs your water is done

Sanitizer readings drop to zero within a day of dosing.
Foam or cloudiness returns within 48 hours of a full treatment.
Persistent dull smell despite shocking.
Water feels sticky or looks flat rather than sparkling.
It's been 4+ months, regardless of appearance.

The refill checklist

A day before draining, run a line purge to strip biofilm while the old water is still in.
Kill power, drain (a submersible pump beats the gravity valve by hours), and wipe the shell with spa surface cleaner.
Deep-clean or replace the filter.
Refill through a hose-end pre-filter, ideally into the filter compartment to purge airlocks.
Power on, heat, then balance in order: alkalinity → pH → calcium hardness → sanitizer.
Shock lightly, run jets, and you're back in that evening.

Don't drain in freezing weather unless you can refill immediately — an empty tub in a New England cold snap risks frozen plumbing.

What you'll need

Line flush / plumbing purgePurging before the drain means the new water starts truly clean.
Submersible drain pumpTurns a 3-hour gravity drain into 20 minutes.
Hose-end pre-filterCleaner fill water means easier chemistry for months.
Spa surface cleanerFor wiping the shell while it's empty.

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Common questions

How often should hot tub water be changed?

Every 3–4 months for typical use, or use the formula: gallons ÷ 3 ÷ daily bathers = days between drains.

Can I just keep adding chemicals instead of draining?

Only up to a point. Dissolved solids accumulate until water stops responding to treatment. When chemicals stop working the way they used to, the water is saturated and needs replacing.

Should I purge the plumbing before draining?

Yes — running a line flush product before draining strips biofilm from the pipes so it doesn't instantly contaminate your fresh fill.

Want exact doses for your tub's volume and sanitizer system? Use the free Spa Assistant — test, enter your readings, get a dosing plan.