By SCWS Team
Published February 17, 2026 · 8 min read
The well screen is where water actually enters your well. This critical component must balance two competing needs: allow maximum water flow while preventing sand and sediment from entering. Get it wrong, and you'll have either restricted flow or sand-damaged equipment.
Well Screen Basics
- Purpose: Allows water in while filtering sand and sediment
- Location: Installed in the aquifer zone (water-bearing formation)
- Key factor: Slot size matched to formation particle size
- Materials: Stainless steel, PVC, or galvanized steel
- Lifespan: 20-50+ years depending on water chemistry and material
Types of Well Screens
Continuous Slot (Wire-Wound) Screen
Considered the premium choice, continuous slot screens are constructed by wrapping triangular wire around a rod frame with precise gaps between wraps. This creates V-shaped openings that are narrow at the outside surface and widen inward.
Advantages: Maximum open area (40-60% vs. 3-10% for slotted pipe), self-cleaning design (particles that enter don't lodge), precise slot sizing, excellent flow capacity.
Best for: High-yield wells, sandy formations, corrosive water (stainless steel versions), professional installations prioritizing long-term performance.
Slotted Pipe
Machine-cut slots in standard pipe create a lower-cost screen option. Slots are typically parallel cuts made with a saw blade.
Advantages: Lower cost, readily available, can be field-fabricated in emergencies.
Disadvantages: Limited open area (5-8%), slots can clog with particles, less precise sizing than wire-wound.
Perforated Pipe
Holes drilled or punched in pipe. The simplest and least expensive option but with significant limitations.
Best for: Consolidated rock formations where large openings aren't problematic, temporary wells, or where formation is naturally well-graded.
Screen Material Selection
Stainless Steel
The premium choice for corrosive or aggressive water. Type 304 stainless handles most conditions; Type 316 provides extra resistance for high-chloride or coastal applications. Lifetime investment that rarely needs replacement.
PVC
Excellent corrosion resistance at lower cost than stainless. Works well in most residential applications with stable formations. Won't handle high temperatures or aggressive physical loads.
Galvanized Steel
Lowest initial cost but shortest lifespan. Zinc coating provides temporary corrosion protection, but eventually fails. Consider for lower-budget applications in non-corrosive water only.
Slot Size Selection
Proper slot sizing is critical—too large and sand enters; too small and flow is restricted. Professional drillers determine slot size through sieve analysis of formation samples.
The goal is to retain approximately 40-60% of the formation material while allowing finer particles through. This creates a natural "gravel pack" around the screen that stabilizes over time.
Common residential slot sizes: 0.010" to 0.030" (slot 10 to slot 30 in industry terminology). Finer slots for fine sand; coarser for gravel formations.
Problems and Solutions
Sand in Well Water
If you're getting sand from your well, possible causes include:
- Screen slots too large for the formation
- Screen damage or corrosion creating holes
- Pump set too low (stirring settled sand)
- Formation collapse around screen
- Excessive pumping rate drawing fine particles
A camera inspection can identify the specific cause. Solutions range from adjusting pump position to well rehabilitation or screen replacement.
Reduced Yield
Declining well yield over time often indicates screen encrustation—mineral buildup or biological fouling blocking the screen openings. This can sometimes be addressed through chemical treatment or mechanical cleaning. Severe cases may require screen replacement.
Frequently Asked Questions
What does a well screen do?
The well screen is the perforated or slotted section of casing installed in the aquifer zone. It allows water to flow into the well while filtering out sand, gravel, and sediment. Without a screen, wells in unconsolidated formations would fill with sand. The screen determines how much water can enter and how much sediment gets through.
Why is there sand in my well water?
Sand in well water usually indicates a screen problem: wrong slot size for the formation (slots too large), screen corrosion or damage creating holes, or a dropped pump disturbing settled sand. It can also indicate formation collapse near the screen. Excessive sand damages pumps and clogs fixtures. A camera inspection can diagnose the cause.
What are the different types of well screens?
Main types include: Continuous slot (wire-wrapped) screens offer maximum open area and are best for high-yield wells. Slotted pipe is less expensive but has less open area. Louver screens direct sand away from openings. Perforated pipe is economical but has limited open area. Material choices include stainless steel, PVC, and galvanized steel.
How is well screen slot size determined?
Slot size is matched to the aquifer formation through sieve analysis—lab testing that determines the particle size distribution of the formation materials. The screen slot size is typically chosen to retain 40-60% of the formation material while allowing finer particles and water through. This creates a natural gravel pack that stabilizes flow.
Screen Problems?
Sand production, reduced yield, and screen corrosion can all be diagnosed and addressed. Camera inspections and well rehabilitation available throughout San Diego and Riverside Counties.
Call (760) 463-0493