Desalination & Membrane Water Treatment Equipment worked example

Spare Membrane Buffer with average membrane element demand of 600 elements / day: a worked example

This worked example runs the spare membrane buffer numbers for a tougher week than the baseline: average membrane element demand of 600 elements / day instead of the typical 1,200 elements / day. Estimate spare membrane element inventory needed to cover replacement demand, supplier lead time, and safety stock for RO, NF, UF, or MF systems.

The inputs for this scenario

  • Average membrane element demand: 600 elements / day (the input this scenario stresses; the baseline uses 1,200)
  • Membrane replenishment lead time: 85 days (held at the documented default)
  • Spare membrane safety stock: 1.1 elements (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Lead-time membrane demand = average membrane element demand × membrane replenishment lead time.
  • Protected days of supply works out to 6.42 days at these inputs, and this is the headline figure for the scenario.
  • Unprotected days works out to 7.06 days at these inputs.
  • Inventory works out to 600 pieces at these inputs.
  • Daily usage works out to 85 pieces / day at these inputs.

How this compares with the baseline

  • Against the tool's baseline example, where average membrane element demand sits at 1,200 elements / day and the headline result is 12.83 days, this scenario comes in 50% below the baseline at 6.42 days.
  • Use it when setting reorder points and safety-stock levels for membrane elements, or when a lead-time quote from your supplier changes. A result at this level usually justifies acting on the stressed input before touching anything else, because every other figure in the table is downstream of it.

Results at a glance

  • Protected days of supply: 6.42 days (headline result)
  • Unprotected days: 7.06 days
  • Inventory: 600 pieces
  • Daily usage: 85 pieces / day

Run it with your numbers

  • To rerun this with your own numbers, open the live Spare Membrane Buffer calculator, set average membrane element demand to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.