Turn a Tarp Into a Water Collection System

Whether you are trying to find out a new survival technique, a camper with a need for water collection, or you want a fun thing to do this weekend that could have a long term benefit on your household, you have come to the right place. A regular waterproof tarp, as found at Tarps.com, can double as a very effective water catcher. All it takes is the right low point, the right drainage gear, and something sturdy to hold the whole thing up.

The Basic Idea

The setup works the same way a funnel does. You create a low point somewhere in the tarp, attach drainage gear to that low point, and let gravity pull the water through the fitting and into a hose, bucket, or storage container. The tarp becomes the catch surface. The drain gear becomes the exit. Everything else is just about keeping the tarp up and sloped so water actually finds its way to that exit instead of pooling somewhere else.

What You'll Need

• A waterproof tarp (poly or vinyl works well — heavier mil weight holds up better to standing water)

• A bulkhead fitting or barbed hose adapter, with a matching washer and nut

• Waterproof silicone caulk

• Metal fittings and metal poles to build a simple frame or support structure

• Ball bungees

• A garden hose and a collection container (bucket, barrel, or cistern)

The frame is where a lot of DIY versions fall apart. A tarp strung between trees or propped on scrap wood will work for a weekend, but if you want something that holds its shape through wind and the weight of collected water, metal fittings paired with metal poles give you a frame that's built for the job.

Setting It Up

1. Cut a hole in the center of the tarp. That, or find the lowest point on the tarp and cut a hole there. An easy way to do that is to pour a bucket of water into that tarp while holding it up and watching where it collects.

2. Cut the drain hole. Cut a hole just big enough for the threaded shaft of your bulkhead fitting or hose adapter to pass through. Smaller is better. You want a tight fit, not a loose one.

3. Lock it down. From underneath, screw the washer and nut onto the fitting and tighten until the tarp material is sandwiched securely between the two pieces.

4. Build your frame. Set up your metal poles and connect them with metal fittings to create a simple frame. Four 1 inch 3-way corner fittings and fo

5. Hang and tension the tarp. Run rope, bungees, or ratchet straps through the corner grommets and secure the tarp to your frame. Pull it tight.

6. Check the slope. Every corner should pull slightly downward and inward toward your drain point. If any section of the tarp sits flat or dips somewhere other than the drain, water will pool there instead of draining and pooled water adds weight fast.

7. Connect your hose. Screw the garden hose onto the underside of the fitting and run the other end into your collection container. From here, gravity does the rest.

Why the Frame Matters

A lot of tarp-based water catchers fail not because of the fitting, but because of what's holding the tarp up. A frame built from metal poles and metal fittings gives you fixed angles and real structural support. This means holding the tarp in a consistent shape, less sag over time, and a setup that can handle a genuine downpour instead of a light drizzle.

It's the same logic that applies to any tarp structure meant to do real work outdoors: the tarp is only as good as what's supporting it. Pair a solid waterproof tarp with the right fittings and poles, and you've got a water collection setup that can hold up season after season, not just until the next storm.

Gathering rainwater is a great way to conserve water and reduce your reliance on municipal water supplies. The collected rainwater can be used for irrigation, washing, and non-potable uses. If you add a water filter to the process, it will ensure you have access to clean drinking water in an emergency. 

The Formula for Rainwater Collection with Tarps

To calculate how much water your tarp can collect, you'll need to know the size of the tarp, the amount of rainfall in your area, and the surface area that will be collecting water. Once you have these three pieces of information, you can use a simple formula to calculate the number of gallons collected by your tarp.

Calculate the amount of rainwater that can be collected in gallons with a simple mathematical formula.

1) Convert square footage into cubic feet by multiplying area (length x width).

    10' x 12' = 120 square feet

2) Convert inches of rainfall to feet using division (inches/12).

     1/2" of rain is (1/2)/12 or .5 divided by 12

     .5 divided by 12 = .042 feet of rain

3) Multiply the two results from Steps 1 & 2 together for total cubic feet of water.

     120 x .042 = 5.04 cubic feet of water

4) Multiply 7.5 gallons per every cubic foot result obtained in Step 3. This is your final answer!

     5.04 cubic feet x 7.5 gallons per cubic foot = 37.8 gallons

So, for every half inch of rain, you would collect 37.8 gallons with a 10' x 12' tarp!

Final Thought

Overall, using tarps for rainwater collection is an easy way to make sure you have access to clean drinking water in a pinch. Plus, tarps are lightweight and easy to store so they're always ready when you need them!

Disclaimer: Always purify your rain water before drinking or use in cooking.