Drill Bits – Water Well Drilling

Tricone Bit vs PDC Bit: Which One Fits Your Water Well?

By Windrilling Technical Team – Updated September 2026 – 10 min read

Last month a water well contractor in northern Ghana sent me a photo of two bits sitting side by side on the tailgate of his pickup. On the left, a 7 7/8 inch tricone with three cones and every insert flattened. On the right, a PDC bit with two chipped blades and a ring of missing cutters.

He had run both in the same hole.

“I want to know which one to buy more of,” he wrote.

The honest answer took forty minutes on the phone, because the answer is not a bit. It is his formation, his rig, his compressor and what he counts as a metre of hole. Give one contractor the tricone and another the PDC in the same rock and both can be the right call.

So here is the same conversation written down. If you are comparing a tricone bit vs PDC bit for a water well programme, this is the order I work through it in.

1. Crushing and Shearing Are Not the Same Job

Everything downstream – bit life, gauge, torque, even how much your compressor has to work – comes out of one difference. A tricone bit breaks rock by loading it again and again until it fails. A PDC bit breaks rock by cutting it.

What a tricone bit actually does

The cones roll. As each tooth or insert comes round it presses into the bottom of the hole, then drags. Rock fails under repeated point loading, and the cuttings get flushed away. Nothing about that action is fussy. The bit does not care whether the interval is hard or soft, it just takes a different amount of weight and time to get through.

That tolerance is why the tricone is still the default bit on so many water wells. Alternating sand and clay, a limestone band, a bit of weathered granite, then a hard stringer – the tricone keeps making hole through all of it. The price you pay is speed, and bearings. Cone bearings and seals are the parts that decide how long the bit lives, and they do not care how sharp the teeth are.

What a PDC bit actually does

No moving cones. Polycrystalline diamond compact cutters are brazed onto fixed blades, and the whole bit is turned slowly under weight. Each cutter shears a sliver of rock off the face. Where the tricone pulverises, the PDC peels.

When it suits the rock, a PDC bit makes rate of penetration look easy, and it can stay in the hole for a long continuous run without a trip. That is the whole commercial argument for a PDC drill bit in water well drilling and it is a real one – on the right interval.

Off that interval it is a brittle, expensive, fixed-cutter tool being hammered by a formation it was not built for. Epiroc’s rotary bit guidance places PDC primarily in oil and gas and horizontal directional drilling, and notes that lower costs have been pushing it into other markets. That wording matters. PDC did not become universal. It became affordable.

2. Formation Fit Decides It, Not Bit Price

Sort the interval before you sort the catalogue. One question does most of the work: does the ground stay the same for a long way, or does it change every few metres?

Ground you are drilling	What I would run	Why
Uniform soft to medium – clay, sand, soft shale, one consistent band	PDC first	Continuous shearing with nothing to chip the cutters. This is the PDC bit’s home ground and where it earns its price
Uniform hard, competent rock	DTH first, PDC only with local proof	Impact beats shear in competent rock. A hard-rock PDC needs evidence from the same formation before you bet a programme on it
Soft and hard interbedded	Tricone	Every change of formation is an impact event. Roller cones tolerate that. Fixed cutters do not
Heavily fractured or faulted rock	Tricone, then evaluate	Fractures and cavities produce shock loads. A tricone is the conservative starting point; no bit fixes a broken rock mass
Overburden into bedrock (the classic water well profile)	Tricone through the top, DTH in the bedrock	Two bits, two jobs. One bit forced to do both is how you end up with the photo on that tailgate

Notice what is not in that table: the word “granite” as a shortcut for “use DTH”. What separates these rows is not the rock name. It is whether the interval is uniform, and how often it changes. Rock that is hard but consistent behaves nothing like rock that is half as hard and full of surprises.

3. What the Rest of Your String Has to Supply

A bit is not a standalone purchase. It is the last 300 mm of a system, and both bit types ask the system for something different.

Requirement	Tricone bit	PDC bit
Rotation	Rig turns the string. Speed is not critical	Needs smooth, steady torque and controlled feed. Rough rotation shows up as cutter damage
Cuttings removal	Air or mud. Cuttings are relatively large, so flow has to be able to lift them	Air or mud, but cleaning is mandatory, not optional. Recirculated cuttings are what destroys a PDC face
Cooling	Friction at the cones. Heat is a bearing problem	Heat is a cutter problem. Poor circulation plus weight is how cutters delaminate
Stability	Tolerant of some string whip	Sensitive to vibration and lateral load. Stabilisation and a straight string matter more
Extra kit	None beyond the rig	None, but the rig’s feed control has to be good enough to use it properly

This is where most disappointing PDC runs are decided, and it is rarely the bit’s fault. If your mud pump is undersized or your hole is not being cleaned, a PDC bit will tell you by failing early. The same undersized pump will let a tricone limp along for months. One bit hides a system problem. The other one exposes it.

If your programme also runs a hammer, the air side has to be sized properly before any of this is worth arguing about. We went through that calculation in detail in our DTH hammer air requirements guide, and the same discipline applies to every bit you put down the hole.

4. Price Per Bit Is Not Cost Per Metre

A tricone bit usually costs less to buy. A PDC bit usually costs more. That is the least useful sentence in this article, because the number that decides whether you made money is cost per metre, and cost per metre has five or six moving parts.

The framework I use with buyers:

Cost per metre = (bit cost + regrind or repair + energy + rig and crew time + trip and bit-change downtime + abnormal losses) ÷ accepted metres

Run the arithmetic on the Ghana hole. The tricone was cheap per bit and needed multiple trips, and every trip costs you the same rig and crew hours whether the bit cost $800 or $4,000. The PDC failed early because the hole was dirty, and an unfinished interval is the most expensive outcome there is: you paid for the bit, the trip, the metres it did not drill, and now you pay for the tricone anyway.

So ask any supplier for four numbers, not one: price per bit, expected accepted metres in your formation, the operating conditions that assumption depends on, and the trip time each bit change costs you. A quotation without the second number is a price, not a recommendation. We have been on both sides of that table and I will take a supplier who says “this bit is wrong for your ground” over one who quotes the cheapest thing in the catalogue.

5. How Each Bit Dies

Wear patterns are the cheapest diagnostic you have. They tell you what your formation is doing to the tool, and whether the next purchase should be a different bit or simply a better-maintained one.

Bit	How rate falls off	What wears	End of life
Tricone	Slowly as teeth dull. Then suddenly, if a bearing goes	Teeth and inserts, then bearings and seals	The cones stop turning reliably, or the bit will not hold gauge
PDC	Gradually under even wear. Sharply when a critical cutter goes	Cutters – chipping, delamination, wear flats – plus gauge pads	It can no longer cut continuously. There is no regrind that brings it back

Two practical consequences. First, a PDC bit has no regrind income and no regrind cost – it is a consumable that ends. A tricone and a DTH bit both live on maintenance discipline, which is why we spend so much time on it: our button bit grinding guide covers the DTH side of that, and the same rule applies here. Check gauge before every run, not after a problem.

Second, gauge failure is a programme-level problem. An under-gauge bit does not just drill a smaller hole. It hands the next bit a reaming job it was never sized for, and if you are setting casing behind it, that is where the cost lands. Gauge checks belong in the same routine as your penetration log.

6. Four Mistakes We See on Water Well Programmes

1. Buying PDC by rate of penetration alone. The fastest bit in a five-metre trial rate is not the cheapest bit over 400 metres. Test on the interval you actually have to drill, not the one that flatters the bit.
2. Running one bit type through the whole borehole. Overburden and bedrock are two different drilling problems. Plenty of contracts are lost by insisting on one bit type for both.
3. Ignoring hole cleaning because the bit “looks fine”. Dirty holes kill PDC cutters and accelerate every other kind of wear. If your cuttings are coming up late or ground up, fix that first.
4. Never weighing a bit. Most crews know the bit failed. Few know whether it was 8 mm under gauge or 2 mm, which is the difference between a normal run and a warning about string alignment. The same field method is covered in our drilling rig troubleshooting guide.

7. What We Supply, and What We Will Not Tell You

We build the rigs and supply the consumables around them. On the bit side that means tricone bits, DTH bits and hammers, drill pipes, rods and shank adapters, plus the air and mud packages that keep them running. You can see the bit range on our drilling tools page or go straight to the TCI tricone bit and the DTH drill bits.

Do we sell PDC bits? No. And I would rather tell you that than sell you the wrong consumable and lose the rest of your programme with it. If your interval is uniform and a PDC is genuinely the right bit, we will tell you what the string around it still has to do, and we will supply the rods, subs, reamers and rig package that make it work. If the answer is a tricone or a DTH bit, that is what we make, and we will match it to your formation and your hammer.

If you already run rotary and want to understand where a hammer would beat your current setup, our DTH vs rotary comparison walks through the same trade-offs from the rig side rather than the bit side.

FAQ

Is a PDC bit faster than a tricone bit?

In a uniform soft to medium interval that suits it, usually yes, and it can hold that rate for a long run. In hard or interbedded rock the advantage narrows or disappears, and the risk of a short run goes up. Speed comparisons only mean something when both bits are running in the same formation with the same rig and the same cleaning.

Can I run a PDC bit in hard rock for a water well?

Hard-rock PDC designs exist and they are used, but published selection guidance treats competent hard rock as a DTH job and asks for formation-specific evidence before trusting a PDC there. Some contractors make it work in specific ground. That is a site-proven decision, not a catalogue decision.

Which bit is cheaper per metre?

There is no fixed answer, and anyone who gives you one before asking about your formation has not thought about it. A tricone has the lower entry price. A PDC gets cheaper per metre the longer it runs without a trip. If it fails early, it is the most expensive bit on the site.

Can I use the same bit for overburden and bedrock?

You can, and a tricone will survive it better than most. You will not get the best cost per metre out of it. The common pattern on a water well is one bit through the overburden and a different one in the bedrock, with the change planned before you spud rather than after something stops working.

Before You Order

Send us five things and we will tell you straight whether you need a tricone, a DTH bit, or neither from us: the borehole diameter and planned depth, the formation you expect through each interval, the rig you are turning and its feed control, how you plan to remove cuttings, and the metres per bit you are getting today. If the answer is a PDC and nothing else, we will say so. If your string cannot support a PDC properly yet, we will tell you what to fix first – because a bit that fails on your site costs us a customer, not a sale.