The first solution card, generated by W7 round 2. Written up first not because it is the most exciting intervention but because it is the cheapest, the most behavioural, and the one with published evidence that current practice is wrong.
What it is
Measure what a pool’s filter actually needs before backwashing it, rather than backwashing on a fixed schedule or by habit. Then set a protocol based on measured water quality, and verify the water consumed per event.
No equipment replacement. In its simplest form this is a change to an operating procedure plus a small amount of instrumentation.
Mechanism
Backwashing flushes the filter to waste. Each event discards a fixed volume of treated, often heated, chemically balanced water. If backwashing happens more often than the filter requires, the excess is pure loss — of water, of the chemicals in it, and of the energy used to heat it. If it happens less often than required, water quality degrades and more chemical correction is needed downstream.
The intervention is to move the trigger from time to condition.
Expected effect
| Metric | Expected change | Range | Tier | Basis |
|---|---|---|---|---|
| Backwash water volume | Reduction | Unknown for private pools | — | No private-pool data exists |
| Sector-level scale of the problem | 5.5 million m³/yr lost in Balearic public pools, ~€13.96 M/yr | — | B | Domènech-Sánchez et al. 2021 |
| Direction of correction | Not necessarily downward | — | B | The same study found protocols inappropriate in most cases and noted that correct practice would require more water in some cases |
Read that last row carefully. This is not reliably a saving. It is a correction. Some pools are wasting water; others are under-backwashing and paying for it in chemistry and water quality. Selling this as a guaranteed saving would violate principle 1. What it reliably delivers is a defensible protocol and a measured number where there was none.
Preconditions
- A pool with a sand or equivalent backwashable filter.
- Willingness to take water quality measurements, or to have them taken.
- A measurable backwash line, or a way to infer volume from duration and flow rate.
When it does NOT apply
- Cartridge filters and other non-backwashing systems.
- Pools where the dominant loss is evaporation or leakage — fix the bigger term first. The point of a water balance is to find out which it is.
- Natural/biological pools, which have a different treatment model entirely.
Cost
| Item | Range | Notes |
|---|---|---|
| Capital cost | Low — test kit or probes for combined chlorine, ammonium, turbidity, COD | Exact spec and cost to be established |
| Installation | Low; a flow meter or timer on the backwash line | |
| Annual running cost | Consumables and time | |
| Annual maintenance | Minimal | |
| Expected lifespan | Indefinite — it is a procedure |
Regulatory position
The 2021 study explicitly calls for specific strategies and legislation covering the management of these installations and the treatment of backwash wastewater. Backwash water is wastewater, and where it goes on a rural property is a live question — see W8. To check against local rules before recommending anything.
Local availability
Deliverable by us, or by any competent pool maintenance provider once the protocol exists. No supply chain dependency. This is unusually good: most interventions need an installer who may not exist on the island.
Side effects and interactions
- Changes chemical consumption, in either direction.
- Changes the volume and composition of wastewater discharged.
- Interacts with heating: discarded water is heated water.
- May surface an unrelated filter or circulation fault, which is a useful side effect.
Failure modes
Under-backwashing degrades water quality and pushes cost into chemistry. The protocol must be conservative until validated on the specific pool.
Measurement plan
- Baseline: current backwash frequency, duration and volume per event; water quality before and after; chemical consumption; make-up water volume.
- Establish the actual condition trigger using the four parameters in K7.
- Set the revised protocol. Pre-register the expected change, in both directions.
- Verify over a full season, normalising for bather load, temperature and rainfall.
Per the evidence protocol. This is a good candidate for an IPMVP retrofit-isolation approach, since the backwash line can be isolated and metered independently of the rest of the site.
Evidence status
- Sector scale and mismanagement: Tier B, published, Balearic-specific — but public pools only.
- Effect on a private finca pool: no evidence at all. Unknown.
Sites where deployed
| Site | Date | Result | Case study |
|---|---|---|---|
| — | Site Zero: candidate for first intervention |