Backwash Refill Cost Calculator

Water loss drivers in backwash cycles

Backwash volume is the baseline refill need, but rinsing can raise it 5–30%. Small overflows during valve changes add 1–5% more. Media type matters: sand and bead filters often need longer rinse than screens. Measure one cycle with a flow meter or timed container fills, then apply that average. Capturing even 10–20% of discharge for irrigation reduces purchased refill water immediately.

Translating volume into monthly and annual refills

Weekly cycles are converted to monthly planning using an average 4.345 weeks per month. For example, 3 cycles per week becomes about 13.0 cycles per month. A 250 L cycle at that frequency uses roughly 3,250 L per month before adjustments. Annual totals help budget peak seasons when algae or fine debris increase cleaning frequency. If your schedule varies, calculate a weighted average across cool and hot months.

Cost structure beyond water tariffs

Many sites pay more than water price alone. If a sewer surcharge applies, it is commonly calculated as a percentage of water charges, even when discharge goes to soil. Pumps also add energy cost; multiply kWh per cycle by cycles and your electricity rate. Chemical conditioners and dechlorinators may be minor per cycle, but significant over a year. Additive costs are easier to estimate when you record dose per refill and unit price.

Labor and downtime as real operating costs

Backwashing often requires supervision, hose positioning, and cleanup. Entering labor minutes converts time to cost using an hourly rate, supporting fair comparisons between manual and automated valves. Tracking labor highlights savings from better pre‑filtration or longer run times between cleanings. Include travel time for offsite gardens, or note opportunity cost during irrigation windows. Documenting these costs supports maintenance planning and contractor quotes.

Using results to reduce waste and improve reliability

Start by exporting CSV or PDF after a representative week. Then test scenarios: reduce rinse percent, add a settling barrel, or increase recovery percent for landscape watering. Compare the per‑cycle cost to decide when to backwash versus replace media or clean mechanically. Watch for cost spikes that indicate leaks, stuck valves, or excessive backwash duration. Consistent tracking helps protect pumps, maintain flow, and control water bills.

FAQs

1) What does “rinse/flush extra volume” mean?

It represents additional water used after backwash to clear dirty water from lines and media. If your system includes a rinse step, add an estimated percentage to reflect that extra refill demand.

2) How can I estimate kWh per cycle?

Multiply pump power in kW by runtime in hours. Example: 0.5 kW running 20 minutes uses 0.5 × 0.333 ≈ 0.167 kWh. Use measured runtime for best accuracy.

3) Should I include sewer charges if discharge goes to the garden?

Use your bill as the rule. If your utility adds sewer as a percent of water use, include it. If you are not billed sewer, set the sewer surcharge to 0%.

4) What is “recovered water” and how do I set it?

Recovered water is the portion you capture and reuse, such as settling and using it for irrigation. Enter only what you truly reuse. Overstating recovery can underestimate real refill cost.

5) Why does the calculator use 4.345 weeks per month?

It is the average weeks in a month across a year (52 weeks ÷ 12 months). This keeps monthly estimates consistent for budgeting, even when individual months have four or five weeks.

6) How often should I update my inputs?

Update whenever tariffs change, the backwash schedule shifts, or equipment is modified. A quick recheck each season is practical, because temperature and debris loads often change filtration behavior.