How to Specify a Water Well Screen: The RFQ Checklist Suppliers Need

What a supplier needs to quote a continuous-slot (Johnson-type) well screen: sieve analysis, well design, water chemistry, connections, standards.

By Serkan İnkaya, Mert Aytünür, Ümit Can Özer, ADEN Wedge Wire · 26 October 2026 · 13 min read

How to specify a water well screen: the short answer

With eight items a supplier can give a real quotation for a water well screen: required flow, installation depth, borehole and casing diameter, slot size or sieve analysis, water analysis, connection type, total length and piece length, and the required standard and certificates. Everything else makes the quotation more accurate and the comparison between bidders fairer.

We wrote this checklist because most well screen enquiries we received in the last months came in with part of this data missing. In one larger tender there was no drawing and no detailed specification, so we could not give a price until the buyer could send one. Some specifications also quoted a withdrawn standard or used a brand name where a screen type was meant. Both are easy to fix at the writing stage.

The checklist applies to stainless continuous-slot wedge wire screens (often called Johnson-type screens), rod-based or pipe-based, for water supply, irrigation and industrial wells.

The well screen RFQ checklist

Copy the groups below into your enquiry or tender. If you do not know a value, write "unknown". The supplier can then state openly which assumption it made.

1. Hydrogeology

1. Sieve analysis of the aquifer, ideally of each screened layer. This is the basis of the slot size. A slot written in the enquiry without the sieve curve cannot be checked by anybody.
2. Aquifer type (confined or unconfined) and aquifer thickness.
3. Depth of the screened interval or intervals.
4. Static water level and expected pumping level.

In a naturally developed well the slot is chosen to retain roughly 40 to 50 percent of the formation sand. In a gravel packed well the slot retains about 90 percent of the pack (100 percent for glass beads). The same aquifer gives two different slots depending on the design, so the supplier needs to know which one you have. Our article on slot size and gravel pack selection explains the method.

2. Well design

5. Borehole (drilling) diameter.
6. Casing diameter and material (carbon steel, stainless, PVC).
7. Gravel pack: yes or no, and the pack grading if already selected.
8. Pump type, pump diameter and design flow.
9. Total depth of the casing and screen column, meaning where the bottom of the screen hangs.

Diameter is driven by the pump and by the upward velocity inside the screen, which should stay at or below about 1.5 m/s. The outside diameter of the connection matters as well: couplings are bigger than the pipe body, and the annulus for the gravel pack is measured from the coupling, not from the screen.

3. Screen

10. Screen type: rod-based continuous slot, pipe-based (screen jacket on a perforated base pipe) or pre-packed.
11. OD or ID, and which of the two is the fixed value.
12. Slot size in mm, or slot number. Slot number is thousandths of an inch: 20 slot is 0.51 mm, 40 slot is 1.02 mm, 60 slot is 1.52 mm.
13. Total screen length and the piece length you want.
14. Material grade (304L, 316L, duplex or other).
15. Collapse and tensile requirement, if you have one, and the basis it is calculated on (see the common mistakes section below).

4. Connections and accessories

16. End connection: weld ring or bevelled end for site welding, flush thread or NPT, BSP thread (used in Europe up to 6 inch), API casing thread (STC or BTC), round thread, tension-proof push-fit coupling with shear rod and O-ring, flange for large diameters, or a transition to PVC casing (DIN 4925 trapezoidal thread).
17. Accessories: bottom plug, sump pipe (usually 3 to 6 m of blank pipe), centralizers, reducers, K-packer for telescoped screens, landing clamp, lifting adapter.
18. If the casing is carbon steel and the screen stainless: does the specification ask for a dielectric coupling or another means of separation? Stainless joined directly to carbon steel in a saturated environment is a galvanic corrosion risk.

5. Water chemistry

19. pH, chloride, H2S, TDS, CO2, dissolved oxygen, iron and temperature.

These values pick the alloy. Commonly cited chloride guide values (Nickel Institute, neutral pH, ambient temperature) are about 200 ppm for 304, 1,000 ppm for 316 and 3,600 ppm for duplex 2205. Corrosive water indicators used in well practice include pH below 7.0, dissolved oxygen above 2 ppm, H2S of 1 ppm or more, TDS above 1,000 ppm, CO2 above 50 ppm and chloride plus bromide plus fluoride above 500 ppm. If you send no analysis, the supplier either picks the safe and more expensive grade or takes a risk on your behalf.

6. Standards and documents

20. Reference standard. For stainless wire-wrapped well screens the current German standard is DIN 4900-2:2017. DIN 4900-1:2017 covers steel casings and their connections. DIN 4935 and DIN 4922 were withdrawn in 2017 and should not appear in new specifications.
21. Material certificate type: EN 10204 3.1 (manufacturer certifies, batch specific) or 3.2 (3.1 plus countersignature by the buyer's inspector or a third party).
22. Third-party inspection: required or not, and by whom.
23. Drinking water approval: say clearly if one is required (for example NSF/ANSI 61, WRAS, KTW or ACS, depending on the country). This changes the supplier list, so it belongs in the first email.

7. Commercial

24. Quantity in metres and in pieces, per diameter and slot.
25. Incoterms 2020 rule and the named place of delivery.
26. Required delivery date at site.
27. Packing requirement (ISPM 15 treated wooden crates, end protectors).

Short version: the minimum eight

What a supplier should send back (the submittal)

A good quotation for a well screen comes with a data sheet, or submittal, per size. Typical fields are taken from established well screen specifications:

• OD, ID and material
• Slot size
• Wire width and wire height (some catalogues call it "wrap-wire length"; ask which one is meant)
• Approximate weight per metre
• Open area in percent and inlet area per metre
• Transmitting capacity per metre, and the entrance velocity it is based on
• Number and diameter of support rods, and total rod cross section
• Yield strength of the material used in the calculation
• Tensile strength, column load and recommended hanging load
• Collapse strength
• For every strength value: whether it includes a safety factor or not

Open area follows a simple formula, open area % = s x 100 / (s + w), with s the slot and w the top width of the wire. It is a gross value. Slots in contact with the gravel pack are always partly blocked, so a transmitting capacity table is good for comparing screens but it is not a guaranteed flow.

Common specification mistakes

A withdrawn standard number

"Screens to DIN 4935" still appears in many tenders. That standard was withdrawn in 2017 and replaced by DIN 4900-2:2017. A supplier who answers "according to DIN 4935" is quoting to a document that no longer exists. Write the current number.

A brand name instead of a screen type

A specification that names one maker's product line ties the tender to that maker. Describe the design instead: continuous-slot, V-shaped wire, resistance welded at every wire and rod intersection, with slot, OD and material. Then add "or approved equal" (see below).

Collapse values without a basis

Published collapse tables do not use the same basis. European tables usually give collapse strength with a safety factor included. US tables give a calculated value without safety factor, and the recommended hanging load there is 50 percent of the calculated tensile strength. Tensile figures also differ: some makers calculate on yield strength of the rods, others on ultimate strength, and on the same rod set the result can differ by a factor of 2.5 to 5. A line like "collapse min. 20 bar" without a basis lets two bidders offer very different screens for the same number.

German practice uses a rough requirement of min. 0.07 bar per metre of installation depth. The same sources call it a rough value used for sizing well pipes, not a structural proof, so it should not stand alone as the design justification in a tender data sheet. A wire-wrapped screen also does not carry axial compression. The column is always installed hanging, never standing on the bottom.

6 m pieces and 20 ft containers

The internal length of a 20 ft container is 5.898 m. A 6 m screen does not fit, and in a crate the practical net length is about 5.7 m. If you ask for 6 m pieces, the shipment goes in a 40 ft container (internal length 12.032 m). The same logic applies to 12 m pipe, which does not fit a 40 ft container once end protectors, length tolerance and crating are added. Ask for piece lengths that fit how the goods will travel, or let the supplier propose.

Entrance velocity written as a hard limit

The 3 cm/s (0.1 ft/s) entrance velocity is a long design tradition in the US and in Europe, and we also use it for capacity calculations. The 2006 edition of AWWA A100 (A100-06) dropped the maximum entrance velocity requirement. Writing it as an acceptance criterion with no tolerance makes bids hard to compare, because screen length and open area can be traded against each other. A design target is fine; a hard limit is debatable.

How to evaluate "or approved equal"

Many well screen tenders are written around one maker's catalogue and end with "or an approved equal". This opens the tender only if the evaluation compares like with like. Check each alternative offer for:

1. The same slot size, measured the same way.
2. Open area calculated with the same formula, on the actual wire width offered.
3. Collapse and tensile strength on the same basis (with or without safety factor, yield or ultimate).
4. The same or a better material grade for the water chemistry.
5. Connection type and coupling OD that fit your borehole and gravel pack annulus.
6. The same certificate type and inspection regime.

If a bidder gives strength values without saying the basis, ask before comparing.

How we handle a well screen enquiry

ADEN Wedge Wire is a wedge wire screen manufacturer based in Istanbul, Turkey, with a European office in Sindelfingen, Germany. When an enquiry reaches us, our engineers check the slot against the sieve analysis, the alloy against the water analysis, and the wire profile against the installation depth. We list every assumption we had to make in the offer. Collapse and tensile values are given as a project-specific calculation on request, with the basis written next to them. Every screen is pickled and passivated after welding, material certificates are supplied, and third-party inspection and customer audits are welcome.

Send us your data

Use our RFQ form or copy the checklist above into an email to info@adenwedgewire.com. Send the sieve analysis, the water analysis and your drawing or specification as attachments; flow, depth, casing size and the other checklist items can go in the form's "Additional Notes" field. Missing data is fine: we tell you which assumptions we made. We reply within 24 hours.

Johnson Screens is a trademark of its owner. ADEN Wedge Wire is not affiliated with Johnson Screens. The term "Johnson-type" is used here only to describe a screen design.

Frequently asked questions

References

1. DIN 4900-2:2017, Brunnenfilter aus nichtrostendem Stahl, DIN
2. EN 10204:2004, Metallic products, types of inspection documents, CEN
3. AWWA A100, Water Wells, American Water Works Association
4. Chloride guidance for stainless steels, Nickel Institute
5. ISO 668, Series 1 freight containers, ISO