Why Water Needs Changing
Hot tub water doesn't last forever despite your best maintenance efforts. Over time, dissolved solids accumulate from body oils, chemicals, minerals, and other sources that filtration cannot remove. Eventually, these accumulations reach levels where water quality becomes difficult to maintain regardless of treatment. Regular water changes reset your spa to fresh conditions.
Understanding when your specific spa needs draining helps you maintain optimal water quality without wasting water through unnecessary changes or suffering poor quality from changes that are too infrequent.
General Guidelines
The common recommendation suggests draining every 3-4 months for typical residential use. This guideline provides a reasonable starting point, but your specific situation may warrant more or less frequent changes. Think of 3-4 months as a baseline to adjust rather than a rigid rule.
Commercial spas with heavy use may require monthly or more frequent changes. Lightly used residential spas might extend to 6 months with proper maintenance. Your usage pattern significantly affects appropriate change frequency.
Usage-Based Calculation
A formula sometimes used divides your spa's gallon capacity by three, then divides by average daily bathers. The result suggests days between changes. For example, a 400-gallon spa with an average of 2 daily bathers: 400÷3÷2 = 67 days, or roughly every 2 months.
This formula accounts for the primary driver of water degradation—bather load introduces the contaminants that accumulate over time. Higher usage requires more frequent changes; lower usage allows extended intervals.
Water Quality Indicators
Beyond schedules, observe your water for signs that changing is due. Cloudy water that doesn't respond to treatment suggests accumulated dissolved solids. Foam that forms easily and persists indicates surfactant buildup. Difficulty maintaining chemistry despite proper treatment points toward water that has simply accumulated too much to manage.
Strong odors, unusual colors, or water that just doesn't feel right also suggest it's time for fresh water. Your sensory observations provide valuable information that supplements testing.
Total Dissolved Solids
Total dissolved solids (TDS) measurement provides objective indication of accumulation levels. TDS above 1500-2000 ppm typically indicates water nearing the end of its useful life. Some test kits and electronic testers measure TDS, providing data to guide change decisions.
Track your TDS over time to understand how quickly it rises in your spa with your usage pattern. This data helps predict when changes will be needed rather than discovering problems after quality has already suffered.
Seasonal Considerations
Many owners align water changes with seasonal transitions—spring and fall provide natural change points that are easy to remember. These transitions also coincide with shifts in usage patterns that make fresh starts appropriate.
Cold climate owners may time fall changes to ensure fresh water before winter when draining becomes more complicated. Spring changes refresh water after potentially heavy winter use. Seasonal scheduling provides structure even if it doesn't perfectly match calculated optimal timing.
The Draining Process
When draining, use the opportunity for thorough cleaning beyond what's possible with water in place. Wipe down surfaces, clean filter housings, and address any areas where buildup has accumulated. This comprehensive cleaning maximizes the benefit of fresh water.
Consider using plumbing flush products before draining to clean internal plumbing that you can't access directly. Biofilm and buildup inside pipes recontaminates fresh water quickly if not addressed during water changes.
Partial Water Changes
Between full changes, partial water replacement can help maintain quality. Draining 6-12 inches and refilling with fresh water dilutes accumulated dissolved solids, extending time between complete changes. Some owners do small partial changes weekly or after heavy use periods.
Partial changes don't replace full draining but can supplement it, particularly during periods of heavier than usual use or when water quality seems to be degrading faster than normal.
Water Conservation
Water changes use significant water—300-500 gallons or more per change. Water-conscious owners balance quality requirements against conservation concerns. Extending change intervals through excellent maintenance, partial changes, and attention to bather hygiene reduces overall water consumption.
Consider directing drained water to landscapes if your chemical levels have been allowed to dissipate—water that's been untreated for a few days typically won't harm plants. Check local regulations regarding spa water discharge if this is a concern in your area.
Establishing Your Schedule
Track your water quality observations, TDS readings if available, and maintenance experiences to determine optimal change frequency for your specific situation. What works for one spa owner may not match your needs given different spa sizes, usage patterns, and maintenance practices.
Start with standard 3-4 month intervals, then adjust based on experience. If you're consistently struggling with water quality before scheduled changes, increase frequency. If water quality remains excellent at change time, you might extend intervals cautiously while monitoring carefully.