Sump: Know your multipurpose water storehouse

One important structure present in every house but often goes unnoticed is the sump tank. Since, municipal water is not provided for construction purposes, Sump became a mandatory structure that has to be erected before commencing any other construction activity. In Bangalore, there are many areas wherein either the frequency of municipal water supply is less or there is no supply at all. Water purchased from private water tankers is stored in sump that acts a supplement to the mandatory overhead tank present in every house.

How to Build a Sump:
Here are some simple guidelines in planning, locating, and constructing the sump.
Location of sump:

Close to the road: the sump location should be located close to the road as the water line runs along the road. Being close to, the road is also advantage when we hire the water tanker to fill-up easily.

Under the porch: Usually sump is planned below the car parking because there is ample space available here and it’s usually near to the road.

According to Vastu: As per Vastu, sump should be located in the Northeast corner of the site. This sometimes needs adjustments in the overall planning of the house in cases where in the site is west facing. Hence, it is recommended that the location of sump is finalized before the architect commences with the actual house plan.

Planning for capacity of sump:
For most families, a sump of 3,000 litres and an overhead tank of 1,500 litres capacity is more than sufficient. However, since a regular tanker load comes with a capacity of 6,000 litres, most of the sumps in Bangalore are constructed with 6,000 litres capacity.
If you are planning more houses for rental purposes then it is suggested that you add the additional capacity of 3000 to 4000 liters per extra house. A bigger sump is more expensive and it takes more space but it is very useful especially when there is a water scarcity.
 Depth of the Sump should be 5 feet and not more because a person should be able to stand in the sump with his head sticking out so that he does not feel suffocated.
 As a rough guide, we should consider that 1 cubic feet area can contain approximately 28 liters of water. So divide the proposed sump capacity with 28 to get the required sump volume in cubic feet and build accordingly.
 Calculate the sump length and breadth by diving the sump volume with the depth. The shape of the sump should be either rectangle or square.

For Example:
If we have decided for a sump capacity with 15000 liters, then divide it by 28 to get a volume of approximately 536 cubic feet. This is the sump volume. Then divide this figure by 5’ depth to get required sump area hich in this case is 107 square feet. Then, decide the length and breadth of the sump based on the shape and available area.

Construction of sump: sump can be constructed by concrete and bricks/blocks depending on capacity of sump.

By using concrete:  Concrete is ideally preferred for constructing the sump because it eliminates problems like water seepage and contamination of the stored water from the soil or underground water or sewage.

By using bricks/blocks: Bricks/blocks are often used owing to cost constraints however there is a risk of leakage. Use of good quality bricks, rough plaster in the outside, and smooth plaster in the inner side of the sump is recommended. Make sure that a plastering mesh is used while plastering to avoid cracks.

 Water pressure will be more on the internal corners of the sump. So avoid constructing the sump/tank corners in 90 degrees like room walls. Instead, have rounded corners so that the water pressure is distributed over a large area and also corners are easier to clean.
 The depth of the sump must be below the depth of the footings.

Case study:

Recently we constructed a sump in a 32’x50’ site where we planned to store 15300 liters of water capacity in a sump. Hence, we excavated the depth as 6’3” from plinth beam bottom with length & breadth of 11’&16’6” respectively.

Construction Process:         
Clean the site
Step 1:- Cleaned the site.
Step 2:- Marked the plot for sump as per above figures.
Step 3:- Filled the area with alternative layers of mud & stones up to 9”. This is called soiling.
Step 4:- Covered the area with PCC (plain concrete cement) in the ratio 0f    1:4:8. Up to 3”.
Step 5:-Steel mat placed for entire area. Mat constructed by using 10 mm rod as rows and columns with the span of 5”.

Step 6:- Covered the area with concrete in the ratio of 1:1.5:3 up to 5”.
Step 7:  Four sides of wall marked with width of 9’3” outer to outer and length of 15’ outer to outer. While marking time we need to leave some space along the outer side walls to fill up wall joints.

Step 8: Raising of Wall:
Height of the wall should be decided based on plinth beam level.
If the plinth beam comes on the top of raised walls then walls should be raised up to plinth beam bottom level. If the plinth beam does not come on top of raised walls then we should raise the walls up to the below the thickness of sump slab which is 5”. In addition, it should be leveled to be beside the plinth beams.
 In this case, we constructed 9” inch walls with length 14’, width 7.75’, and depth/height 5’ inner to inner. Hence, we can store approximately 15,300 liters of water.


Step 9: Plastering
=> Mesh to be placed:
PVC pipe conduits for rain water or electric wiring placed inside the masonry walls where plaster has tendency to shrink and crack. To prevent this, prior to plastering, a chicken wire mesh should be wrapped around the PVC conduit. Similarly, chicken wire should be placed over the brick work junction to prevent hairline crack in plaster.
=> First, we plastered one layer of cement mortar mix in the ratio of 1:3 and then attached a chicken mesh. After that we left it for one day for drying. Waterproofing chemical should be added to the mortar mix (140 ml for one bag of cement). Also check that the mortar is not hollow at corners.
=> The walls are then plastered with 1:4 Mortar mix, Rounded corners, as recommended earlier, are made while plastering.
Step 10: Curing:
Curing is mandatory to any structural member. Hence we should cure the walls, sump bottom surface, and top surface for two days. And finally we can store the water in sump.


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