How to Let Wet Sand Through Without Letting Water Through

Most people arrive here after configuring a Filter to allow wet sand, watching the wet sand fall through correctly, and watching the water come with it. Nothing is broken. You have asked a filter to do the one thing filters explicitly do not do.

Why the basic Filter cannot work

The Filter’s own permeability stats are unambiguous:

	Blocks it
Liquid	No
Gas	No
Player	Yes

Water is a liquid. It passes through a Filter regardless of whether you set Allow or Block, and regardless of which material you name. There is no configuration that changes this, so there is no point hunting for one.

For the record, the buildings that do stop water are: Block, Conveyor Belt, Kinetic Press, and Flux Emanator. Water passes through everything else, filters very much included.

Fix the cause: stop making surplus water

Before building anything, check whether you need to separate them at all.

Sand and water combine exactly one-for-one: Official1 Sand + 1 Water becomes 2 Wet Sand. Water that is still liquid downstream of your washer is water that had no sand to bond with. It is surplus you created.

Meter your water intake to match your sand throughput and the problem disappears — no filter, no research, no gold. This is the fix that scales, because every alternative below is you paying to clean up water you did not need to add.

The free fix: put it on a conveyor belt

Before spending anything, use the belt you already have.

A Conveyor Belt is documented as Blocks Liquid: Yes — water cannot fall through it. And water behaves differently on a belt than solids do: Officialliquids ignore a belt’s direction of travel and flow across it as they would over any other ground.

Those two facts together are the separation. Drop your mixed flow onto a run of belt:

1. Wet sand is carried in the belt’s direction, because it is a solid pixel sitting on the belt surface.
2. Water is not carried. It spreads and runs off by gravity instead of travelling with the sand.
3. Put your Filter at the far end of the belt, past the point where the water has drained away, and it only ever sees wet sand — so Allow Wet Sand works exactly as you expected it to in the first place.

Give the water somewhere to go at the near end — a gap, a pit, a return to your washer — or it pools on the belt and stalls the line.

When you actually need to filter the liquid itself

Belt drainage handles the common case. If you genuinely need the water routed rather than drained — recycling it back into the washer, say, or working with mixed liquids — the Advanced Filter is the building that can act on liquids at all.

• Research tier: 4
• Cost: 1,500 Gold
• No prerequisites beyond reaching the tier

Spend the 1,500 Gold when you want the water somewhere specific. If you only want it gone, the belt already did the job.

The jam that will bite you on the way there

While sand and water are still sharing a path, there is a specific failure worth knowing about, because it looks like a game bug and it is not.

If a material that your Filter allows through changes into a different material while it is passing through, it sticks. It stops falling, and the conveyor part of the Filter will not push it along either. You have to remove it by hand.

The common case is exactly your situation: sand riding a Filter meets water falling through the same Filter, becomes wet sand mid-transit, and wedges there. Every stuck pixel narrows the line until the whole thing stalls.

Keeping water and dry sand on separate paths until you want them to meet is not tidiness — it is what stops your factory seizing up.

Two more things about water

Density decides stacking order. Water sits at 100, wet sand at 150. In a mixed pile the wet sand is underneath and the water rides on top. That is useful whenever you are working with piles rather than flows: the thing you want is already at the bottom, which is where filters pull from.

Loose water evaporates. A droplet that does not settle into a depression within 45 seconds disappears. Small amounts of stray water often resolve themselves — worth knowing before you build a drainage system for a puddle.

Related

• Sandustry Beginner Guide — the sand-to-gold loop this sits inside, and what to research first
• How to break Crackstone — the other early wall with a documented answer rather than a workaround