How-To Guides | Draining Your Spa - When, How & Why

Most spa owners change their hot tub's water every 2 to 4 months. Over time, salts from sweat and other non-organic materials build up in the water. These Total Dissolved Solids, or TDS, cause cloudiness or other problems.

Even though organic materials like skin cells & bacteria are destroyed by your hot tub shock, TDS levels still increase. But how do you really know when it's time for draining?

Water lasts much longer when you properly maintain your pH, Total Alkalinity, chemicals & filters. When the TDS level exceeds about 1500 PPM, it's time to change the water. These levels can be checked with TDS test strips or a TDS meter.

Estimating How Long Between Water Changes

Use your manual to figure out how many gallons are in your spa. Determine the estimated number of days between water changes:

Bather Load

Bather load is the average amount of people in your hot tub per day. More users per day will need more frequent water changes.

  • Estimate how many times your spa was used in the last month
  • Multiply by number of users
  • Divide by 30 days

For example, if you used your spa 15 times last month with yourself and 3 friends:

  • 15 times x 4 people = 60
  • 60 / 30 days = 2
  • That's an average of 2 people in the spa per day

Time Between Draining

  • Divide your total spa gallons by 3
  • Divide by the bather load

For example, if you have a 300 gallon spa and our bather load above of 2 people/day:

  • 300gal / 3 = 100
  • 100 / 2 = 50

That's 50 days between changes, or about 7 weeks. A larger spa or one with less frequent use will have a longer amount of time between refills.

These are only estimates. We assume that your hot tub water is properly balanced and sanitized.

The cleanliness of your bathers & your local water quality will also affect time between drain intervals. If you shower before using the spa, water will stay cleaner, longer.

Local regulations & ordinances sometimes do not allow frequent water replacement. Many commercial spas are required to drain more frequently due to a high bather load.

Hot Tub Drains

Most spas have a drain faucet, or bib, inside the access panel. A few older or inflatable hot tubs have no drain and have to be emptied with a hose siphon.

Newer spa models feature an external drain, allowing easy draining by attaching a garden hose.

If your spa lacks a drain, or it is difficult to access, consider a draining pump. Our HydroMaster Water Drain Pumps flow 330 gallons per hour, outperforming simple gravity siphons many times over.

Flush Your Spa's Plumbing with Every Water Change

You do your best to keep your spa clean. What you don't know is that the INSIDE of your spa's plumbing system is coated with oily film & contaminants.

Always flush your hot tub plumbing, jets and heater before draining with Spa System Flush. You will have the cleanest possible water and get more time between refills..


"We use it daily to vacuum gritty sand from the bottom of the spa.  There was no easy way to get it out before.  Although our spa has its own drain, using the Shake-a-Vac at the same time empties the water twice as fast."

Randy Parkhurst
Lincoln, NB


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