You can buy commercial sand and water tables anywhere, and many of them cost the same as my DIY model. So why would you want to build one?
First of all, aesthetics. You will likely want to keep your sensory table in a non-carpeted area, and possibly near a sink. That often means your shared living space. And if you're like me, you don't want your house to look overrun with toys. Those colourful plastic things are great for outdoor play but kind of an eyesore in your kitchen. This sensory table has a nice solid wood design that can be stained to match your decor.
Secondly, the DIY design is versatile. Look at this Step 2 commercial water table. It looks like fun, but what can your child do with it? Their dolls can swim and frolic in water. That is it. There is no room for any creative play. The design dictates exactly what they are to do with it.
The "open concept" sensory bin has unlimited uses. We have used them for rice, cloud dough, corn meal, corn starch, cereal, pasta, paint, sand, water, slime, flubber, goop, rocks, mud, eggs, cereal, cake mix, and dozens of other things that you would never dare to put in your fancy palm tree water table. The best part is, if you make a mess that stains or tarnishes your bin, you can easily designate that bin the "messy" one and insert a new bin. You can also store multiple bins full of sensory materials and just trade them up whenever your little one needs a change.
The first thing you need to do is to purchase storage containers. I like to have more than one so I can store dry sensory materials in them. I chose 25 and 41 Qt. Sterilite Containers from Walmart because they are very affordable and they have a relatively flat bottom. The dimensions listed are specific to those exact containers. If you choose a different container you will have to estimate the sizes based on the width half way up the container, due to the sides being beveled.
Start by building your lower (inner) frame out of 2.5" by 3/4" wood. Assemble it with wood glue and small nails.
Next add your longer pieces out of 3.5" wood and attach them to the outside, offset by about 2.25 inches to hold your bin in place. Then add the end pieces by measuring the sides after they are attached.
Next, you will add the legs, the length of which will vary depending on the height of the child. If you are making this for a classroom, measure your smallest child so that the top of the bin will fall just below chest level. Taller children can sit to use the table.
Sand it very well so children do not get splinters. My sensory table has rounded down edges for added safety. Lastly, add a water resistant varnish or paint.