Planning pools, ponds and water storage

Almost every water project starts with a volume. The size of the pump, the amount of salt or chemicals, the liner, the weight of the water and the time it takes to fill all come from how many gallons there are. Get the volume right and the rest follows.

This planner covers swimming pools, ponds, tanks and pipes, rainwater collection and the equipment that heats or softens household water.

Step 1: Work out the volume

Pools and ponds are rarely perfect rectangles, so split them into shapes and use the average depth. Tanks and pipes use the cylinder formula. A cubic foot holds 7.48 gallons and weighs about 62 pounds, so large volumes are heavy.

Step 2: Size the pump and filter

The pump must turn over the whole volume of a pool in about 8 hours, and the filter and pipes must handle that flow. A variable-speed pump saves a great deal of electricity. For a pond, the pump should turn over the water about once an hour.

Step 3: Salt and chemistry

A saltwater pool generator needs a set salt level for the pool volume, and the salt is added in bags. Test the water regularly and follow the equipment maker's guidance for chemicals.

Step 4: Collect and store rainwater

A roof sheds a lot of water: a quarter inch of rain on 1,000 square feet of roof gives well over 100 gallons. Size the barrels or tank for the roof area, the rainfall, and your use. Untreated rainwater is for watering the garden, not for drinking.

Step 5: Hot water and softening

A tankless water heater is sized by the flow in gallons per minute and the temperature rise. A water softener is sized by the hardness of the water and the daily use.

Before you start

• The permit, fencing and safety rules for a pool, which are strict in most places.
• Call 811 before you dig.
• The electrical work, which must be done by a licensed electrician with GFCI protection.
• A drain and overflow plan for the water.
• The weight of water and equipment on the ground or the deck.

Mistakes that cost people money

• Guessing the pool volume, then over- or under-dosing salt and chemicals.
• Oversizing the pump so it wastes power and strains the filter.
• Forgetting that water is heavy when planning a tank or a pond on a deck.
• Drinking untreated rainwater.
• Skipping the safety fencing and covers.

Frequently asked questions